Generation of diversity in combinatorial libraries

ABSTRACT

The invention concerns gene banks and combinatorial derivatives thereof, prepared using phagemid- or phage-display in combination with type IIS restriction enzymes and cosmid packaging; their use for the isolation of ligands, including enzyme inhibitors, agonists and antagonists for receptors, competitive binding peptides to a defined target, diagnostic ligands for diseases and autoimmune syndromes, including surveillance tools for immune status, post-translationally modified peptides, and such ligands generated by this technology.

This is a continuation of International Application No. PCT/EP98/00533 filed Feb. 2, 1998, the entire disclosure of which is incorporated herein by reference.

Biotech evolutionary methods, including combinatorial libraries and phage-display technology (PARMLEY & SMITH 1988; SCOTT & SMITH 1990; SMITH 1993), are used in the search for novel ligands of diagnostic, biomedical and pharmaceutical use (reviews; CORTESE 1996; COLLINS 1997). These methods, which use empirical procedures to select molecules with required characteristics, e.g. binding properties, from large populations of variant gene products has been compared to the process of natural evolution. Evolution includes the generation of mutation, selection of functionality over a time period and the ability of the systems to self-replicate. In particular natural systems use recombination to reassort mutations accumulated in the selected population to exponentially increase the combinations of mutations and thus increase the number of variants in the population. This latter aspect, namely the introduction of recombination within mutant genes has only recently been applied to biotech evolutionary methods, although it has been used to increase the size of initial phage-display libraries (e.g. WATERHOUSE 1993; TSURUSHITA 1996; SODOYER 1994; FISCH 1996). STEMMER 1994a, 1994b and 1995 teach that recombination amongst a population of DNA molecules can be acheived in vitro by PCR amplification of a mixture of small overlapping fragments with (1994a, 1994b) or without (STEMMER 1995) primer oligonucleotide sequences being used to drive the PCR reaction. The method is not applicable to recombination within a fully randomized (highly mutated) sequence since the method relies on high homology of the overlapping sequences at the site of recombination. STEMMER 1994b and CRAMERI 1996a do, however, demonstrate the usefulness of in vitro recombination for molecular evolution, where CRAMERI 1996b also demonstrate the use of the method in conjunction with phage-display, even though their method is confined to regions of low mutant density (ca. 0.5-1% of the bases are mutated in their method) as they state “the advantages of recombination over existing mutagenesis methods are likely to increase with the numbers of cycles of molecular evolution” (STEMMER 1994b). We point out that this is due to the self-evident fact that the number of variants created by mutagenesis introducing base changes in existing mutant structures is an additive i.e., a linearly increasing function, whereas the use of recombination between mutated variants yields novel variants as an exponential function of the initial number of variants. The classical phage-display libraries are thus at a grave disadvantage for the generation of novel variants; e.g. to encompass all the possible variants of an octapeptide sequence 20⁸=2.56×10¹⁰ different variants would be required.

MARKS 1992 state the importance of recombination in the generation of higher specificity in combinatorial libraries e.g. in attaining antibodies of higher specificity and binding constants in the form of reshuffling light and heavy chains of immunoglobulins displayed in phage-display libraries. These authors do not instruct how the shuffling of all the light and heavy chains in a population heterogeneous in both chains can be acheived, e.g. by a vector allowing recombination. Heavy and light chains were selected one after the other, i.e. an optimal heavy chain first selected from a heterogenous heavy chain population in the presence of a constant light chain, then by preparing a new library, an optimal light chain in combination with the preselected optimal heavy chain. The extensive time consuming sequential optimization strategies currently utilized including consensus-mutational libraries, in vivo mutagenesis, error-pone PCR as well as chain shuffling are summarized in FIGS. 5 and 6 of COLLINS 1997.

General Background to Phage and Phage-display Libraries

Gene libraries are generated containing extremely large number (10⁶ to 10¹⁰) of variants. The variant gene segments are fused to a coat protein gene of a filamentous bacteriophage (e.g. M13, fd or f1), and the fusion gene is inserted into the genome of the phage or of a phagemid. A phagemid is defined as a plasmid containing the packaging and replication origin of the filamentous bacteriophage. This latter property allows the packaging of the phagemid genome into a phage coat when it is present in an Escherichia coli host strain infected with a filamentous phage (superinfection). The packaged particles produced, be they phage or phagemid, display the fusion protein on the surface of the particles secreted into the medium. Such packaged particles are able to inject their genomes into a new host bacterium, where they can be propagated as phage or plasmids, respectively. The special property of the system lies in the the fact that since the packaging takes place in individual cells usually infected by a single variant phage/phagemid, the particles produced on propagation contain the gene encoding the particular variant displayed on the particle's surface. Several cycles of affinity selection for clones exhibiting the required properties due to the particular property of the variant protein displayed, e.g. binding to a particular target molecule immobilized on a surface, followed by amplification of the enriched clones leads to the isolation of a small number of different clones having these properties. The primary structure of these variants can then be rapidly elucidated by sequencing the hypermutated segment of the variant gene.

Efficiency of Producing Combinatorial Libraries

There are a number of factors which limit the potential of this technology. The first is the number and diversity of the variants which can be generated in the primary library. Most libraries have been generated by transformation of ligated DNA preparations into Escherichia coli by electroporation. This gives an efficiency of ca. 0.1 to 1×10⁶ recombinants/microgram ligated phage DNA. The highest cloning efficiency reported (of 10⁷ recombinants per microgram insert DNA) is obtained using special lambda vectors into which a single filamentous phage vector is inserted, in a special cloning site, bracketted by a duplication of the filamentous phage replication/packaging origin (AMBERG 1993; HOGREFE 1993a+b). The DNA construct is efficiently introduced into the Escherichia coli host after packaging into a lambda bacteriophage coat in an in vi tro lambda packaging mix. Infection of a strain carrying such a hybrid phagemid by an M13- helper phage allows excision and secretion of the insert packed in a filamentous phage coat. Neither AMBERG 1993 nor HOGREFE 1993a+b instruct on how the method may be used to introduce recombination during this procedure. Although they mention that the efficiency may be improved by the use of type IIs restriction endonucleases during the construction of the concatemers used as substrate for the in vitro packageing no examples are given and in the ensuing five years no examples have appeared in the literature. The procedure described in our invention also uses the high efficiency of the invitro lambda packaging , but maximizes the capacity of the cloning vector by using a cosmid vector (8) in which many copies (say 8) of the phagemid are inserted in each construct. One of the surprising innovative aspects of this procedure is the discovery of a number of protocols for the de novo synthesis of large hypervariable libraries. One type is particularly efficient, in that phagemid/cosmid vectors are forced to integrate into the hybrid concatamers oriented in the same orientation. Any variant of the protocol which does not ensure this feature does not work efficiently.

The Use of Type IIs Restriction Endonucleases

SZYBALSKI 1991 teaches a large number of novel applications for type IIs restriction endonucleases, including precise trimming of DNA, retrieval of cloned DNA, gene assembly, use as a universal restriction enzyme, cleavage of single-stranded DNA, detection of point mutations, tandem amplification, printing amplification reactions and localisation of methylated bases. They do not give any instruction as to how such enzymes can be used in the creation of recombination within highly mutated regions, e.g. within a combinatorial library.

Reference List

Amberg, J, Hogrefe, H., Lovejoy, H., Hay, B., Shopes, B, Mullinax, R. and Sorge, J. A.(1993), Strategies, 5, 2-3.

Collins, J. (1997) Phage display. In Moos, W. H. et al. (eds) Annual reports in combinatorial chemistry and molecular diversity. Vol. 1., ESCOM Science publ., Leiden. pp. 210-262.

Cortese, R.(ed.) (1996) Combinatorial libraries: Synthesis, Screening and Application potential. Walter de Gruyter, Berlin.

Crameri, A., Whitehorn, E. A., Tate, E. and Stemmer, W. P. C. (1996a) 14, 315-319.

Crameri, A., Cwirla, S. and Stemmer, W. P. C. (1996b) Nat. Med. 2, pg. 100.

Fisch, I., Kontermann, R. E., Finnern, R., Hartley, O., Soler-Gonzalez, A. S., Griffiths, A. D. and Winter, G. (1996) Proc. Natn. Acad. Sci. USA. 93, 7761.

Marks, J. D.; Griffiths, A. D.; Malmqvist, M.; Clackson, T. P.; Bye, J. M. and Winter, G. (1992) BioTechnol. 10, 779-783.

Hogrefe, H. H., Amberg, J. R., Hay, B. N., Sorge, J. A. and Shopes, B. (1993) Gene, 137, 85-91.

Hogrefe, H. H., Mullinax, R. L., Lovejoy, A. E., Hay, B. N. and Sorge, J. A. (1993) Gene 128, 119-126.

Parmley, S. F. and Smith, G. P. (1988) Gene 73, 305-318 Scott, J. K. and Smith, G. P. (1990) Science 249, 386-390 Smith, G. P. (1993) Gene 128, 1-2.

Sodoyer, R., Aujume, L., Geoffrey, F., Pion, C., Puebez, I., Montegue, B., Jacquemot, P. and Dubayle, J. (1996) In Kay, B. K. et al. (eds.) Phage display of peptides and proteins. A laboratory manual. Academic Press, San Diego. Pp. 215-226 Stemmer, W. P. C. (1994a) Nature (Lond.) 370, 389-391 Stemmer, W. P. C. (1994b) Proc. Nat. Acad Sci. USA, 91, 10747-10751 Stemmer , W. P. C (1995) Gene 164, 49-53 Szybalski, W., Kim, S. C., Hasan, N. and Podhajska, A. J. (1991) Gene, 100, 13-26.

Tsurushita, M., Fu, H. and Warren, C. (1996) Gene, 172, 59. Waterhouse, P. , Griffiths, A. D., Johnson, K. S. and Winter, G. (1993a) Nucleic Acid Res. 2265-2269.

According to a first embodiment the invention concerns a bank of genes, wherein said genes comprise a double stranded DNA sequence which is represented by the following formula of one of their strands:

5′B₁B₂B₃ . . . B_(n)X_(n+1) . . . X_(n+a)Z_(n+a+1)Z_(n+a+2)X_(n+a+3) . . . X_(n+a+b)Q_(n+a+b+1) . . . Q_(n+a+b+j+)3′

wherein n, a, b and j are integers and

n>3, a>1, b>3 and j>1,

wherein X_(n+1) . . . X_(n+a+b) is a hypervariable sequence and B, X, Z and Q represent adenine (A), cytosine (C), guanine (G) or thymine (T),

(i) Z represents G or T at a G:T ratio of about 1:1, and/or

(ii) Z represents C or T at a C:T ratio of about 1:1, and/or

(iii) Z represents A or G at a A:G ratio of about 1:1, and/or

(iv) Z represents A or C at a A:C ratio of about 1:1, and wherein

subsequences B₁ . . . B_(n) and/or Q_(n+a+b+1) . . . Q_(n+a+b+j) represent recognition sites for restriction enzymes, and wherein the recognition sites are orientated such that their cleavage site upon cleavage generates a cohesive end including the two bases designated Z.

Restriction of this sequence with a type IIs restriction enzyme as thus described, followed by religation leads to the recombination of the hypervariable regions located 5′ and 3′ of the cleavage site. This is the essence of the methodology which we designate “cosmix-plexing”. It is essential in this procedure that the fragments generated on cleavage by the restriction enzyme are religated in the correct orientation(“head-to-tail”), whereby the Z sequences are chosen for the four libraries ((i) to iv)) so as to ensure this (see below) yet still allowing all possible amino-acids to be encoded at the cleavage site. If this correct orientation is not ensured there will be a drastic reduction in both the percent of correctly reconstituted fusion-protein genes, a reduction in the proportion of molecules which can be packaged in vitro in the lambda-packaging extracts (which requires the correct orientation of the cos-sites), as well as a reduction in the proportion of in vivo excisable phagemid copies from the cosmid concatemer (excision requires the correct orientation of consecutive phage replication origins) correct orientation correct orientation incorrect orientation (head-to-head ligation)

To prevent the problems arising from false orientation (head-to-head) mentioned in the previous paragraph, the four gene libraries mentioned in claim must be kept separated during cosmix-plexing. In fact with respect to the formation of recombinants the libraries behave as 16 separate sets which cannot recombine with each other: four libraries maintained separately, where each set contains four possible cohesive ends, e.g. library (i) with Z=G or T contains:

It is evident that problems of false orientation will arise on mixing the different libraries, e.g. the “AC library (iv) will contain AA, AC, CA and CC sequences which can pair in the false orientation with, respectively each of the cohesive ends generated in library (i).

A specific embodiment of the invention concerns a bank of genes wherein subsequences B₁ . . . B_(n) or Q_(n+a+b+1) . . . Q_(n+a+b+j) represent recognition sites for restriction enzymes and wherein the recognition sites are orientated such that their cleavage site upon cleavage generates a cohesive end including the two bases designated Z.

Further, a specific embodiment concerns a bank of genes, wherein the cohesive end is a 2 bp single strand end formed by the two bases designated Z.

Further, a specific embodiment concerns a bank of genes wherein each gene is provided as display vector, especially as M13 phage or M13 like phage or as phagemid.

Another embodiment of the invention concerns a set of four gene banks according to the invention wherein the gene banks are characterized as follows:

first gene bank: Z represents G or T, preferentially at a

G:T ratio of about 1:1;

second gene bank: Z represents C or T, preferantially at a

C:T ratio of about 1:1;

third gene bank: Z represents A or G, preferentially at a

A:G ratio of about 1:1; and

fourth gene bank: Z represents A or C, preferentially at a

A:C ratio of about 1:1.

A specific embodiment of the invention concerns a set of four gene banks wherein each gene is provided as display vector, especially as M13 phage or M13 like phage or as phagemid.

Another embodiment of the invention concerns a bank of genes wherein said genes comprise a double stranded DNA sequence which is represented by the following formula of one of their strands:

5′B₁B₂B₃ . . . B_(n)X_(n+)1 . . . X_(n+a)Z_(n+a+1)Z_(n+a+2)X_(n+a+3) . . . X_(n+a+b)Q_(n+a+b+1) . . . Q_(n+a+b+j)3′

wherein n, a, b and j are integers and

n>3, a>1, b>3 and i>1,

wherein X_(n+1) . . . X_(n+a+b) is a hypervariable sequence and B, X, Z and Q represent adenine (A), cytosine (C), guanine (G) or thymine (T), and wherein

four sets of oligonucleotide sequences comprising Z_(n+a+1) and Z_(n+a+2) are present, preferentially at a ratio of (i):(ii):(iii):(iv) of about 1:1:2:2, wherein the four sets are characterized as follows:

first set: Z_(n+a+1) represents G and Z_(n+a+2) also represents G;

second set: Z_(n+a+1) represents C and Z_(n+a+2) represents T;

third set: Z_(n+a+1) represents A and Z_(n+a+2) represents A or C, preferentially at A:C ratio of about 1:1; and

fourth set: Z_(n+a+1) represents T and Z_(n+a+2) represents C or G, preferentially at a C:G ratio of about 1:1, and wherein

sequences B₁ . . . B_(n) and/or Q_(n+a+b+1) . . . Q_(n+a+b+j) represent recognition sites for restriction enzymes, wherein the recognition sites are orientated such that their cleavage site upon cleavage generates a cohesive end including the two bases designated Z.

A specific embodiment of the invention concerns a bank of genes wherein the four sets of oligonucleotide sequences are present at a ratio of (i):(ii):(iii):(iv) of (0 to 1):(0 to 1):(0 to 1):(0 to 1) with the proviso that at least one of said sets is present.

Further, a specific embodiment of the invention concerns a bank of genes wherein subsequences B₁ . . . B_(n) and/or Q_(n+a+b+1) . . . Q_(n+a+b+j) represent recognition sites for restriction enzymes and wherein the recognition sites are orientated such that their cleavage site upon cleavage generates a cohesive end including the two bases designated Z.

Furhter, a specific embodiment of the invention concerns a bank of genes wherein the cohesive end is a 2 bp single strand end formed by the two bases designated Z.

Another embodiment of the invention concerns bank of genes wherein said genes comprise a double stranded DNA sequence which is represented by the following formular of one of their strands:

5′B₁B₂B₃ . . . B_(n)X_(n+1) . . . X_(n+a)Z_(n+a+1)Z_(n+a+2)X_(n+a+3) . . . X_(n+a+b)Q_(n+a+b+). . . Q_(n+a+b+j)3′

wherein n, a, b and j are integers and

n>3, a>1, b>3 and j>1,

wherein X_(n+1) . . . X_(n+a+b) is a hypervariable sequence and B, X, Z and Q represent adenine (A), cytosine (C), guanine (G) or thymine (T), and wherein

the following six sets of oligonucleotide sequences comprising Xn+a, Z_(n+a+1) and Z_(n+a+2) are present, preferably at a ratio of (i):(ii):(iii):(iv):(v):(vi) of about 3:4:3:4:4:1, wherein the six sets are characterized as follows:

first set: X_(n+a) represents A, G and/or T, preferentially at a ratio of about 1:1:1 or X_(n+a) represents C, G and/or T, preferentially at a ratio of about 1:1:1, Z_(n+a+1) represents G and Z_(n+a+2) represents G;

second set: X_(n+a) represents A, C, G and/or T, preferentially at a ratio of about 1:1:1:1, Z_(n+a+1) represents C and Z_(n+a+2) represents T;

third set: X_(n+a) represents A, C and/or G, preferentially at a ratio of about 1:1:1, Z_(n+a+1) represents A and Z_(n+a+2) represents A;

fourth set: X_(n+a) represents A, C, G and/or T, preferentially at a ratio of about 1:1:1:1, Z_(n+a+1) represents A and Z_(n+a+2) represents C;

fifth set: X_(n+a) represents A, C, G and/or T, preferentially at a ratio of about 1:1:1:1, Z_(n+a+1) represents T and Z_(n+a+2) represents C;

sixth set: X_(n+a) represents A, Z_(n+a+1) represents T and Z_(n+a+2) represents G.

“Single-tube” Method

Problem

A method should be developed which allows cosmix-plexing without maintaining separate libraries. This would have the advantage of reducing manipulation, involved in screening the four separate libraries, as previously described. This would offer a saving in both time and materials. This has been acheived in two separate versions of the invention.

Solution

It is possible to select combinations of nucleotides within the cohesive ends generated by type IIs restriction within the aforementioned sequence, i.e. ZZ, in which all the clones are present in a single library and in which the possibility of false orientation during ligation, and the associated loss of efficiency associated with this, is eliminated. At the same time the number of subsets, defined by the number of different cohesive ends which can be generated, which cannot interact (recombine) with each other, is reduced from the 16 sets, as in the previously described version of the method, to 6.

Designing the Sequences

The combinations of 2 bp single-strand cohesive end sequences which can be generated at ZZ are theoretically as follows:

AA CA GA TA AC CC GC TC AG CG GG TG AT CT GT TT

Of these, the sequences with an inverted symmetry axis (palindromes: AT, TA, GC, CG ), can pair in both orientations and are thus to be eliminated from cosmix-plexing libraries for the reasons given above. The remaining 12 sequences are actually 6 sets of complementary pairs (e.g. CC+GG, AA+TT, CA+TG). By choosing one partner from each pair (total of 6) a single set of cohesive ends can be generated which can pair only in the correct “head-to-tail” orientation. The actual choice of sequences takes the codon usage into account, assuming that ZZ are chosen as the 2nd and 3rd position of the codon. Determining are the amino-acids which are encoded by either a single or only two codons (single codon methionine (TG) and tryptophan (GG); after elimination of the palindromic sequences there also only single codons available encoding aspartic acid (Asp), asparagine (Asn), cystine (Cys), histidine (His) and tyrosine (Tyr). To encode Asp, Asn, His and Tyr an AC sequence is required. Selecting AC has the default that the complimentary sequence GT must be avoided. This is the only possibility of encoding Cys. However, the inclusion of Cys within the hypervariable sequence often causes problems of misfolding and the formation of dimeric aggregates, dependent on the redox potential of the environment. It was thus decided to create a set in which Cys codons are eliminated, but which will be of great use in many applications, including cyclic peptide library formation. If the sequence AA is chosen to encode glutamic acid (Glu), glutamine (Gln) and lysine (Lysl also allowing the stop-codon TAA, then TT must be eliminated. The consequence of this is that TC must also be included so that phenylalanine (Phe) and isoleucine (Ile) can be encoded. The elimination of the complimentary GA is without consequence since other GG codon(s) encode argenine (Arg) and glycine (Gly). The elimination of CC is then without consequence, since alanine (Ala), proline (Pro), serine (Ser) and threonine (Thr) can be encoded by CT-containing codons. This is the argumentation for the selection of ZZ sequences designated “combination A” below.

For the sake of completeness: if the doublet AA were left out and, consequently TT included, then AG must be included to encode Glu, Gln and Lys. In order to encode Ala and Pro, either CT (combination B) or CA (combination C) must now be included. This leads to the inclusion of either AG and CT (combi. B), or CA and TG (combi. C) as complimentary pairs. Combinations B and C thus do not represent an adequate solution to the problem.

combination A combination B combination C AA TT AA TT AA TT AC GT AC GT AC GT AG CT AG CT AG CT CA TG CA TG CA TG CC GG CC GG CC GG GA TC GA TC GA TC

Sequences chosen are shown in bold type. Complementary pairs are adjacent to each other.

TABLE 1 Genetic code; the selection of XZZ codons used according to combination A is shown in bold type. Ala Arg Asp Asn Cys Glu Gln Gly His Ile Leu GCA AGA GAC AAC TGC GAA CAA GGA CAC ATA TTA GCC AGG GAT AAT TGT GAG CAG GGC CAT ATC TTG GCG CGA                     GGG     ATT CTA GCT CGC                     GGT         CTC     CGG                                 CTG     CGT                                 CTT Lys Met Phe Pro Ser Thr Trp Tyr Val Stop AAA ATG TTC CCA AGC ACA TGG TAC GTA TAA AAG     TTT CCC AGT ACC     TAT GTC TAG             CCG TCA ACG         GTG TGA             CCT TCC ACT         GTT                 TCG                 TCT

TABLE 2 Frequency of the amino-acids, comparing the selected combination A (above) and the natural frequency of all codons. Amino-acid natural frequency Combination A Ala 4 1 Arg 6 2 Asp 2 1 Asn 2 1 Cys 2 0 Glu 2 1 Gln 2 1 Gly 4 1 His 2 1 Ile 3 1 Leu 6 3 Lys 2 1 Met 1 1 Phe 2 1 Pro 4 1 Ser 6 1 Thr 4 1 Trp 1 1 Tyr 2 1 Val 4 2 Stop 3 1 Total 21 64 24

Creation of a Set of Four Oligonucleotides According to Combination A

Gene libraries can be created according the requirements of the combination A, by creating four sets of nucleotides in which X_(n+a)Z_(n+a+1)Z_(n+a+2) are:

i) NGG

ii) NCT

iii) NA(A or C)

iv) NT (C or G),

where N is C,G,A or T.

After the synthesis of these oligonucleotides they can be combined to obtain a single-tube cosmix-plexing gene library, whereby to obtain the relative codon frequencies given in Table 2 the gene libraries i) to iv) are present in the final mixture at a ratio of 1:1:2:2, respectively. As explained above this mixture will always give a correct orientation on religation of type IIs restriction enzyme-cleaved fragments having the 2bp single-stranded cohesive ends ZZ.

Alternatively: a Set of Six Oligonucleotides Conforming to Combination A

Gene libraries can be created according a modification of combination A, in which both Stop and cystine codons are eliminated, and in which each of the other amino-acids is each represented by a single codon, by creating six sets of nucleotides in which X_(n+a)Z_(n+a+1)Z_(n+a+2) are:

i) (A, G or T)GG or (C,G or T)GG

ii) NCT

iii) (A, G or C)AA

iv) NAC

v) NTC

vi) ATG

After the synthesis of these oligonucleotides they can be combined to obtain a single-tube cosmix-plexing gene library, whereby to obtain the equimolar codon frequencies for each amino-acid the gene libraries i) to vi) are present in the final mixture at a ratio of 3:4:3:4:4:4: 1 respectively. As explained above this mixture will always give a correct orientation on religation of type IIs restriction enzyme-cleaved fragments having the 2bp single-stranded cohesive ends ZZ.

Again, as with the previous sets this single-tube library represents six-subsets which are unable to recombine with each other during cosmix-plexing.

*** the following section has been altered radically. The last Tables are no longer necessary.

Consideration of the Central Amino-acid Codon Created During Cosmix-plexing Recombination

The amino-acid at the recombination site is determined by the 5′-hypervariable segment. The set of amino-acids which may be represented at this position is defined for each subset as presented in Table 2.

Consideration of the Number of Clones Needed in a “Representative” Library

The minimal number of clones required in a library to include all possible amino-acid sequences in a random peptide containing ‘n’ amino-acids is 20^(n), i.e. for n=9, 20⁹=5.12×10¹¹. In fact, at a confidence limit of say 95%, this figure must be some three-fold higher, to allow for the statistics of sampling, i.e. ca. 1.5×10¹². In practice this figure may be higher due to, e.g. non-random synthesis of the oligonucleotides used to generate the library as well as biased codon representation (for a detailed discussion see Collins 1997).

Consideration of the Number of Recombined Clones Generated by Cosmix-plexing

The cosmix-plexing strategy is based on the concept that in initial selection experiments clone populations will be enriched for sequences which contain structural elements based on the primary sequence in the varied segment. Even if the optimal sequence is not present due to the limitations imposed by the limited size of the initial library. cosmix-plexing will increase the likelihood of finding just such a sequence by providing a large number of novel recombinants in which the 5′- and 3′-“halves” of the varied section are reassorted e.g. for the hypervariable nonapeptide library described in the example, the sequences encoding the amino-proximal five amino acids are recombined with the sequences encoding the carboxy-proximal four amino-acids. Since the cohesive ends essentially limit the recombination to defined subsets, in which one subset cannot undergo recombination with any of the other subsets, the actual number of recombinants generated is less than could be obtained with completely random recombination.

For the initial four-tube protocol described, four separate libraries each containing four subsets are used:

Random recombination would generate, for a set of N clones, N² recombinants, assuming N² is less than or equal to the theoretical number of variants (20^(n) see above) which can be encoded within the hypervariable segment, otherwise it will tend to 20^(n).

For the four-tube protocol 16 subsets are created each representing a pool within which recombination can take place. If the total the library consists of N clones then the number of novel recombinants which can be formed within each of the 16 subsets is (N/16)². Summing for all sixteen subsets, the number of recombinants which can be generated is 16×(N/6)²=N²/16, again assuming N²/16 is less than or equal to the theoretical number of variants (20^(n), see above) which can be encoded within the hypervariable segment, otherwise it will tend to 20^(n).

For the single-tube protocol only 6 subsets are created. each representing a pool within which recombination can take place. If the total library consists of N clones then the number of novel recombinants which can be formed within each of the 6 subsets is (N/6)². Summing for all six subsets, the number of recombinants which can be generated is 6×(N/6)²=N²/6, again assuming N²/6 is less than or equal to the theoretical number of variants (20^(n), see above) which can be encoded within the hypervariable segment, otherwise it will tend to 20^(n).

It is thus clear that the single-tube version of the invention is superior not only in terms of time and economy of the procedure but in the potential to generate a greater diversity from a given number of clones during cosmix-plexing guided recombination.

A specific embodiment of the invention concerns a bank of genes, wherein the six sets of oligonucleotide sequences are present at a ratio of (i):(ii):(iii):(iv):(v):(vi) of (0 to 1):(0 to 1):(0 to 1):(0 to 1):(0 to 1):(0 to 1) with the proviso that at least one of said sets is present.

Further, a specific embodiment of the invention concerns a bank of genes wherein each gene is provided as display vector, especially as M13 phage or M13 like phage or as phagemid.

Further, a specific embodiment of the invention concerns a bank of genes wherein the double stranded DNA sequence is comprised by a DNA region (fusB) encoding a peptide or a protein to be displayed.

Further, a specific embodiment of the invention concerns a bank of genes, characterized in that n=j=6, a=14 and b=16.

Further, a specific embodiment of the invention concerns a bank of genes wherein the restriction enzyme is a tyoe IIS restriction enzyme.

Further, a specific embodiment of the invention concerns a bank of genes which is characterized in that

(a) subsequence B₁ . . . B_(n) is the recognition site for the restriction enzyme BpmI (CTGGAG) and subsequence Q_(n+a+b+1) . . . Q_(n+a+b+j) is an inverted BsgI recognition site (CTGCAC); or

(b) subsequence B₁. . . B_(n) is the recognition site for the re-striction enzyme BsgI (GTGCAG) and subsequence Q_(n+a+b+1) . . . Q_(n+a+b+j) is an inverted BpmI recognition site (CTCCAG).

Further, a specific embodiment of the invention concerns a bank of genes which is characterized in that the hypervariable sequence X_(n+1) . . . X_(n+a+b) contains NNB or NNK wherein

N=adenine (A), cytoseine (C), guanine (G) or thymine (T);

B=cytosine (C), guanine (G) or thymine (T); and

K=guanine (G) or thymine (T).

Another embodiment of the invention concerns a phagemid pROCOS4/7 of the sequence shown in FIG. 6.

Still another embodiment of the invention concerns a phagemid pROCOS5/3 of the sequence shown in FIG. 7.

Another embodiment of the invention concerns a method for the production of large

phage-display libraries or

phagemid-display libraries,

 containing or consisting of optionally packaged recombined display vectors, wherein recombination takes place at the cleavage site(s) for a restriction enzyme (cut (B) enzyme; arrow in FIG. 3) and wherein

(a) to (b) a double-stranded DNA prepared from Escherichia coli cells containing a display vector population, consisting of M13 phages or M13 like phages or consisting of phagemids according to the invention; a cosmid vector; a restriction enzyme for cut (B); and a restriction enzyme for cut (A) are selected, wherein

(i) the cut (B) enzyme cleaves the display vectors in the region encoding the displayed peptide or displayed protein (arrow in FIG. 3) and generates unique non-symmetrical cohesive ends, wherein each cohesive end is a 2 bp single strand end formed by the two bases designated Z, and

(ii) the cut (A) enzyme cleaves the display vectors and the cosmid vector and generates upon cleavage unique non-symmetrical cohesive ends (fusA) which differ from those resulting from cut (B),

(c) the display vectors are cleaved with the first restriction enzyme,

(d) the display vector and the cosmid vector are cleaved with the second restriction enzyme,

(e) the cleaved display vectors are ligated with the cleaved cosmid vectors forming concatamers,

(f) the ligation product is subjected to a lambda packaging and transduced into an Escherichia coli host,

(g) if wanted, selection is made for a gene present in the ligated display vectors,

(h) the transduced display vectors in the Escherichia coli host are

either in the case of a phage-display vector spontaneously packaged in M13 or M13 like phage coats

or in the case of a phagemid-display vector packaged by infecting the Escherichia coli host with an M13 type helper phage (superinfection),

(i) the packaged display vectors are passaged in a fresh Escherichia coli host and phage-display or phagemid-display libraries are formed and, if wanted,

(j) the passaged display vectors are

either in the case of a phage-display vector spontaneously packaged in M13 or M13 like phage coats or in the case of a phagemid-display vector packaged by infecting the fresh Escherichia coli host with an M13 type helper phage (superinfection) and

 phage-display or phagemid-display libraries are formed.

A specific embodiment of the invention concerns a method which is characterized in that in steps (a) to (b) a type IIS restriction enzyme is selected, preferably BglI, DraIII, BsgI or BpmI.

Further, a specific embodiment of the invention concerns a method which is characterized in that for cuts (B) and (A) the same restriction and/or restriction enzyme is selected.

Further, a specific embodiment of the invention concerns a method which is characterized in that as cut (B) enzyme and as cut (A) enzyme different enzymes are used (FIG. 3), preferably BsgI or BpmI as cut (B) enzyme and DraIII as cut (A) enzyme (fd or M13 replication origin cut).

Further, a specific embodiment of the inven tion concerns a method which is characterized characterized in that in step (h) and facultatively in step (j) M13K07 is used as M13 type helper phage.

Further, a specific embodiment of the invention concerns a method which is characterized in that characterized in that the ophagemid and the cosmid are identical and, further, presence of and cleavage with cut (A) enzyme is optional and/or cut (B) enzyme and cut (A) enzyme are identical.

Further, a specific embodiment of the invention concerns a method which is characterized in that in step (i) the multiplicity Qf infection (MOI) is less than or equal to

Further, a specific embodiment of the invention concerns a method wherein the cosmid comprises an fd or M13 bacteriophage origin (replication/packaging).

Further, a specific embodiment of the invention concerns a method wherein in step (e) a mol ratio of display vectors to the cosmid vector within the range of from 3:1 to 15:1 and preferably 3:1 to 10:1 is used.

Further, a specific embodiment of the invention concerns a method wherein in step (e) a vector concentration (comprising display vectors and cosmid vectors) of more than 100 μg DNA/ml is used.

Another embodiment of the invention concerns a method for the production of large

phage-display extension libraries or

phagemid-display extension libraries, wherein

 an oligonucleotide cassette of d bases in length is inserted into a restriction site (cut (B)) via the cohesive ends ZZ as defined above to yield a sequence (supra sequence) or a gene comprising a double stranded DNA sequence which is represented by the following formula of one of their strands:

5′B₁B_(n)X_(n+1) X_(n+a)Z_(n+a+1)Z_(n+a+2)X_(n+a+3)X_(n+a+d)Z_(n+a+d+1)Z_(n+a+d+2)X_(n+a+d+3)X_(n+a+d+b)Q_(n+a+d+b+1)Q_(n+a+d+b+j+)3′

wherein d is an integer and a multiple of 3, preferably within the range of from 6 to 36; n, a, b and j and B, X, Z and Q have the same meaning as in any of the preceding claims; and wherein

(a) to (b) a double-stranded DNA prepared from Escherichia coli cells containing a display vector population, consisting of M13 phages or M13 like phages or consisting of phagemids according to the invention; a cosmid vector; a restriction enzyme for cut (B); and a restriction enzyme for cut (A) are selected, wherein

(i) the cut (B) enzyme cleaves the display vectors in the region encoding the displayed peptide or displayed protein and generates unique non-symmetrical cohesive ends; wherein each cohesive end is a 2 bp single strand end formed by the two bases designated Z,

(ii) the cut (A) enzyme cleaves the display vectors and the cosmid vector such that unique non-symmetrical cohesive ends are formed which differ from those resulting from cut (B),

(c1) the display vectors are cut with the cut (B) restriction enzyme,

(c2) a DNA cassette is inserted into the cleavage site with their ZZ cohesive ends,

(d) the resulting display vector and the cosmid vector are cleaved with the cut (A) restriction enzyme,

(e) the cleaved display vectors are ligated with the cleaved cosmid vectors forming concatamers,

(f) the ligation product is subjected to a lambda packaging and transduced into an Escherichia coli host such that the DNA cassette lies betweeen two hypervariable sequences (extension sequences),

(g) if wanted, selection is made for a gene present in the ligated display vectors,

(h) the transduced display vectors in the Escherichia coli host are

either in the case of a phage-display vector spontaneously packaged in M13 or M13 like phage coats

or in the case of a phagemid-display vector packaged by infecting the Escherichia coli host with an M13 type helper phage (superinfection),

(i) the packaged display vectors are passaged in a fresh Escherichia coli host and phage-display or phagemid-display libraries are formed, and, if wanted,

(j) the passaged display vectors are

either in the case of a phage-display vector spontaneously packaged in M13 or M13 like phage coats

or in the case of a phagemid-display vector packaged by infecting the fresh Escherichia coli host with M13 type helper phages (superinfection) and

Phage-display or Phagemid-display Extension Libraries are Formed.

Another embodiment of the invention concerns a method for the reassortment of the 5′- and/or 3′-extensions in the production of large recombinant

phage-display extension libraries or

phagemid-display extension libraries,

 comprising the sequence as defined before wherein recombination takes place at one or the other, or consecutively at both the cleavage site(s) ZZ bracketting the inserted cassette(s), wherein

(a) to (b) a double-stranded DNA prepared from Escherichia coli cells containing a display vector population, consisting of M13 phages or M13-like phages or consisting of phagemids as display vectors as defined before; a cosmid vector; a restriction enzyme for cut (B); and restriction enzyme for cut (A) are selected, wherein

(i) the cut (B) enzyme cleaves the display vectors in the region encoding the displayed peptide or displayed protein and generates unique non-symmetrical cohesive ends at selectively either

the 5′-junction of extension and cassette (cleavage by the restriction enzyme recognizing the binding site B₁ . . . B_(n) as defined before), or

at the 3′-junction of extension and cassette (cleavage by the restriction enzyme recognizing the binding site Q_(n+a+b+1) . . . Q_(n+a+b+j) as defined before, or Q_(n+a+d+b+1) . . . Q_(n+a+d+b+j) as defined before), wherein each cohesive end is a 2 bp single strand end formed by the two bases designated Z,

(ii) the cut (A) enzyme cleaves the display vectors and the cosmid vector and generates upon cleavage unique non-symmetrical cohesive ends which differ from those resulting from cut (B),

(b) the display vectors are cleaved with the first restriction enzyme,

(c) the display vector and the cosmid vector are cleaved with the second restriction enzyme,

(e) the cleaved display vectors are ligated with the cleaved cosmid vectors forming concatemers,

(f) the ligation product is subjected to a lambda packaging and transduced into an Escherichia coli host,

(g) if wanted, selection is made for a gene present in the ligated display vectors,

(h) the transduced display vectors in the Escherichia coli host are

either in the case of a phage-display vector spontaneously packaged in M13 or M13-like phage coats

or in the case of phagemid-display vectors packaged by infecting the Escherichia coli host with an M13-type helper bacteriophage (superinfection),

(i) the packaged display vectors are passaged in a fresh Escherichia coli host and phage-display or phagemid-display libraries are formed and, if wanted

(j) the passaged display vectors are

either in the case of a phage-display vector spontaneously packaged in an M13 or M13-like phage coats

or in the case of a phagemid vector packaged by infecting the fresh Escherichia coli host with M13 type helper phages (superinfection) and

Phage-display or Phagemid-display Libraries are Formed.

A specific embodiment of the invention concerns a method which is characterized in that in steps (a) to (b) a type IIs restriction enzyme is selected, preferably BgII, DraIII, BsgI or BpmI.

Further, a specific embodiment of the invention concerns a method which is characterized in that for cuts (i) and (ii) the same restriction site is selected.

Further, a specific embodiment of the invention concerns a method which is characterized in that as cut (B) enzyme and as cut (A) enzyme different enzymes are used, preferably BsgI or BpmI as cut (B) enzyme and DraIII as cut (A) enzyme (fd or M13 replication origin is cut).

Further, a specific embodiment of the invention concerns a method which is characterized in that in step (h) and facultatively in step (j) M13K07 is used as the M13-type helper phage.

Further, a specific embodiment of the invention concerns a method which is characterized in that in step (g) selection is made for the presence of an antibiotic resistance gene.

Further, a specific embodiment of the invention concerns a method which is characterized in that in step (i) the multiplicity of infection (MOI) is less than or equal to

Further, a specific embodiment of the invention concerns a method wherein the cosmid comprises an fd or M13 bacteriophage origin.

Further, a specific embodiment of the invention concerns a method wherein in step (e) a mol ratio of display vectors to the cosmid vector within the range 3:1 to 15:1 and preferably 3:1 to 10:1 is used.

Further, a specific embodiment of the invention concerns a method wherein in step (e) a vector concentration (comprising display vectors and cosmid vectors) of more than 100 μg DNA/ml is used.

Another embodiment of the invention concerns a method for the de novo production of large

phage-display libraries or

phagemid-display libraries,

 comprising DNA sequences aa defined before, and subjectable to recombination according to a procedure as defined before, wherein recombination takes place within a DNA sequence as defined before, wherein

a) a display vector, consisting of an M13 phage or M13- like phage or consisting of a phagemid-display vector comprising a bacteriophage replication origin, facultatively a gene for a selectable marker, preferably an antibiotic resistance, a lambda bacteriophage cos-site and a “stuffer” sequence (FIG. 5 upper right), containing two binding sites for a type IIs restriction enzyme different from any of the enzymes as defined before (cut (B) and cut (A)), wherein said two sites are oriented in divergent orientation and where the cohesive ends generated on cleavage are non-symmetrical and differ from one another at the two sites, and

b) a PCR-generated fragment comprising part of one of the sequences as defined before, including a (the) hypervariable sequence(s), preferably X_(n+1) . . . X_(n+a)Z_(n+a+1)Z_(n+a+2)X_(n+a+3) . . . X_(n+a+b) according to the invention, bracketted by the same type IIs restriction enzyme binding sites defined in (a), but in this case both oriented inwards towards the hypervariable sequence (FIG. 5 left side) and where on cleavage by this restriction enzyme two non-symmetrical, single strand ends different from one another are generated, where the first end (a′ in FIG. 5) is complementary to one of the ends (a in FIG. 5) generated on the large vector fragment in (a) and the second end (b′ in FIG. 5) is complementary to the other end (b in FIG. 5) generated on the large vector fragment in (a),

c) the two cleavage reaction systems (a) and (b) still containing the active type IIs restriction enzyme are mixed together in approximately equimolar proportions and subjected to ligation in the presence of DNA ligase;

 fragments containing the restriction enzyme binding sites are constantly removed (“stuffer” fragment and outer end of the PCR product) whereas

 the other two components, namely the large vector fragment and the insert sequence (central fragment from the PCR reaction) are driven to form

A) a concatameric hybrid if the ligation is carried out at >100 μg DNA/ml (FIG. 5), or

B) a circular hybrid if the ligation is carried out at <or=40 μg DNA/ml,

d1) in the case of protocol A) the DNA is packaged into lambda particles and transduced into an Escherichia coli host,

d2) in the case of protocol B) the DNA is transformed in an Escherichia coli host,

e) if wanted, selection is made for a gene present in the ligated display vectors,

f) the transduced display vectors in the Escherichia coli host are

either in the case of a phage-display vector spontaneously packaged in M13 or M13-like phage coats

or in the case of phagemid-display vectors packaged by infecting the Escherichia coli host with an M13-type helper bacteriophage (superinfection),

(g) the packaged display vectors are passaged in a fresh Escherichia coli host and phage-display or phagemid-display libraries are formed and, if wanted

(h) the passaged display vectors are

either in the case of a phage-display vector spontaneously packaged in an M13 or M13-like phage coats

or in the case of a phagemid vector packaged by infecting the fresh Escherichia coli host with M13-type helper phages (superinfection) and

Phage-display or Phagemid-display Libraries are Formed.

A specific embodiment of the invention concerns a method which is characterized in that in steps (a) to (b), as type IIs restriction enzyme, preferably BpiI, BsgI or BpmI is selected.

Further, a specif ic embodiment of the invention concerns a method which is characterized in that in step (f) and facultatively in step (h) M13K07 is used as the M13-type helper phage.

Further, a specific embodiment of the invention concerns a method which is characterized in that in step (e) selection is made for the presence of an antibiotic resistance gene.

Further, a specific embodiment of the invention concerns a method which is characterized in that in step (g) the multiplicity of infection (MOI) is less than or equal to 1.

Another embodiment of the invention concerns a phage-display library or a phagemid-display library in the form of packaged particles obtainable according to any of the methods as described before.

Another embodiment of the invention concerns a phage-display library or a phagemid-display library in the form of display vectors comprised by Escherichia coli population(s) obtainable according to any of the methods a s described before.

Another embodiment of the invention concerns a phage-display libraries or phagemid libraries which are characterized by a gene (genes) as defined before and obtainable according to the invention, wherein the term “large” as used before is defined as in excess of 10⁶ variant clones, preferentially 10⁸ to 10¹¹ variant clones.

Finally, another embodiment of the invention concerns a protein or peptide comprising a peptide sequence encoded by a DNA sequence as defined before and obtainable by affinity selection procedures on a defined target by means of a from libraries as defined before.

DETAILED DESCRIPTION

The invention pertains to a novel combination of recombinant DNA technologies to produce large hypervariable gene banks for the selection of novel ligands of pharmaceutical, diagnostic, biotechnological, veterinary, agricultural and biomedical importance with an efficiency higher than was hitherto attainable.

The size of the hypervariable gene bank is presently considered the most essential factor limiting the usefullness of the methodology for such purposes, since, as an empirical method, it depends on the diversity (number of different variants) initially generated in the bank (hypervariable gene library). In contrast to this traditional opinion we consider that, when a highly efficient method is developed, as presented here, to generate a large proportion of the possible combinations of mutated segments of the variants from a preselected subpopulation, a population enriched for the desired structural elements will be generated which would only have been represented in a population approaching N^(x) where N is the size of the original population and x is the number of segments to be recombined.

The first part of the invention pertains to novel sequences which allow recombination within hypervariable DNA sequences encoding regions (domains) variable peptides or proteins displayed in combinatorial phage/phagemid display libraries using type IIs restriction endonucleases both (a) to introduce a cut at the site of recombination and (b) to generate oriented substrates for a ligation reaction, where the ligation products are then recloned at high efficiency after in vitro packaging in a lambda packaging mix. The entire protocol yields efficiencies (clones per input DNA) in excess of any described technology (>10⁸ clones per microgram ligated DNA).

Combinations of (vector)sequences and protocols are claimed for both the production of the initial librairies and for recombinational procedures to generate increased diversity within the library or a selected subpopulation at any time. In particular such sequences and procedures are claimed for the generation and use of phage/phagemid-display combinatorial libraries.

The inventors recognise that the main factor thereby determing the efficient generation of further variation is the efficient production of combinatorial libraries from the initial libraries, via reassortment of smaller elements (specific peptide sequences within the hypervariable region, and/or reassortment of structural domains) which contribute to the properties selected for. The invention presents such a method, which has the unique property that the recombination site may be within the hypervariable region whereby no restriction is imposed on the sequence within the hypervariable region involved. Alternatively the method can be used to reassort domains of proteins or subunits of heteromeric proteins (proteins composed of two or more different variant polypeptide chains), each of which can contain hypervariable regions, without resorting to recloning isolated DNA fragments or generating new libraries containing new synthetic oligonucleotides. It is noted that this method thus offers a saving in both time and materials when optimizing a structure for a predetermined property on the basis of a preselected clone population (subpopulation) and in view of the geometrical increase in possible variability offered may represent a qualitatively novel feature in that some rare structures may be obtainable only by the novel strategy described.

The method, we designate cosmix-plexing⁷, is based on the design of the cloning vectors, the inserts used and a combination of special recombinant DNA protocols, which in particular use i) cleavage of the phage/phagemid DNA with type IIs restriction enzymes, ii) subsequent ligation to concatamers which are iii) packaged in vitro with a lambda packaging system for iv) efficient transduction into E. coli strains, where they are then v) repackaged in vivo in filamentous phage coats. The use of cosmix-plexing⁷, so defined, on a heterogeneous phage/phagemid population generates an enormous increase in novel variants at any time during further experimentation, e.g. after any enrichment step for structures having the predetermined property or properties.

In particular subpopulations which are enriched from the original library for a specific property will be enriched for a consensus motif (a degenerate set of related sequences within the varied region(s) which all exhibit the required property to some extent) which may (probably will) include the optimal sequence in terms of the required property. Reassortment of these regions or portions of a single hypervariable sequence by cosmix-plexing⁷ will increase the probability of obtaining the optimal sequence. The subpopulations may be isolated by differential affinity-based selection on a defined target, or enrichment procedures based on other desired selectable properties (example 1: substrate properties such as phosphorylation by a particular protein kinase enriched by binding on antibodies which recognise the modified (in this case phosphorylated) substrate; or example 2: cleavage of the variant sequence by an endoprotease, using selective release of the phage or phagemid previously bound via an interaction between a terminal protein structure(anchor) and its ligand immobilised to, or later trapped on, a surface).

The invention further covers the generation of extension libraries in which e.g. a “project-specific cassette” is inserted at the recombination site within the gene bank. Optimisation of ligands can then occur by the generation of further combinatorial libraries from selected clones in which the adjacent regions may be efficiently “shuffled”, either singly or both at a time. As far as we are aware no other system provides this “cassette” insertion/exchange” feature.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1. Diagrammatic representation of the steps involved in creating recombination within the hypervariable regions of cosmix-plexing7 libraries.

Double-stranded phagemid from a number of clones (which may be a cosmid itself) and cosmid DNA(if the phagemid is not a cosmid) are cleaved with a type IIs restriction enzyme (cleavage sites indicated by a small bar) within the hypervariable region and ligated together at high DNA concentration so that long concatemers of the DNA molecules are formed, which are all oriented in the same direction, e.g with respect to the M13 packaging origins, i.e. no palindromic regions are formed. The vectors contain one or more restriction site(s) for the type IIs restriction enzyme such that no cohesive ends are formed which on ligation could form palindromic (i.e. head-to-head or tail-to-tail) structures. When the cohesive ends produced on cleavage by the restriction enzyme are themselves non-palindromic and unique to each restriction site within each plasmid/phagemid, only ring closure and the formation of concatemers can be formed. At higher DNA concentrations (i.e. over 200 μg/ml) concatemer formation will be preferred. A more detailed presentation of the molecular structures formed is given in FIGS. 2 and 3. The ligation product is added to an in vitro lambda packaging extract where the DNA is packaged into a lambda bacteriophage coat as a linear DNA of 37 to 50 kb cleaved at a lambda cossite. In the following step, referred to as transduction, these particles carrying the cosmid-phagemid hybrid DNA are added to Escherichia coli cells (shown as large ellipses in the diagram) into which the DNA injects itself. In the cell it is circularized by closure of the cleaved cos-site using the endogenous DNA ligase. It is then propagated as a large cosmid-phagemid hybrid, replicating from the plasmid DNA replication origin(s). M13-type helper phage (e.g. M13K07) is added to these cells in the step referred to as superinfection. On entry of the helper phage single strand replication is initiated from the M13 replication origins present in the individual copies of the phagemid contained in the concatemer. During this process the phage are also packaged into M13 coats, and secreted into the medium. The phagemid can be harvested from the supernatant of the culture. A second passage, i.e. transduction into an E. coli host and repackaging by superinfection with helper phage is necessary before these phagemid are used in a selection procedure in order to ensure that a particular variant protein is presented only on the particle carrying the gene for that particular variant protein. It is noted that this is a highly efficient process in which a yield of more than 10⁸ different phagemid can be produced pro microgram of ligated input DNA.

FIG. 2. The diagram illustrates the DNA structures formed when the cosmix-plexing7 protocol is carried out as shown in FIG. 1. Different variants are designated by different patterns for the whole plasmid. Initially double-stranded DNA is cleaved with a type IIs restriction enzyme A. The ligation product is illustrated as a concatemer in which each phagemid is oriented in the same orientation. The products of 37 to 50 kb introduced after in vitro lambda packing and introduction into the E. coli cells (shaded ellipses) are shown, whereby, for example 8 to 10 copies of a 4.5 kb phagemid may be present per cell. On repackaging the same phagemid are obtained as were present before cleavage and ligation. The protocol as shown here in which the M13-packaging/replication site and the restriction site for enzyme A are identical, is simply an efficient method of amplification when starting with double stranded DNA.

FIG. 3. The diagram illustrates a variant of the protocol illustrated in FIGS. 1 and 2 in which recombination is achieved between different phagemid variants. The cross-over point for the recombination is the cleavage site for the type IIs restriction enzyme B (shown as a hollow arrow) cleaving preferentially within a hypervariable region or between two different variable regions (see also FIG. 4, where additional cleavage sites within other variable regions may be recombined simultaneously). Again, as mentioned in the FIG. 1 legend, each phagemid may be a cosmid itself, in which case the addition of another cosmid is unnecessary. In this example cleavage with the restriction enzyme A is optional. Although FIGS. 2 and 3 are almost identical it should be noted that the products of the scheme in FIG. 3 are all recombined, i.e. hybrids of the two sides of different variants. Repassaging is needed before use in the recombined library for selection experiments for the same reasons discussed in the previous two Figures.

FIG. 4. Cosmix-plexing7 Strategies.

The left part of the figure shows the hypervariable DNA sequences encoding the variable portion of the peptide or protein presented on the phage/phagemid. The four bars designated ‘N variants’ show that there are different sequences on either side of the type IIs restriction cleavage site. Phagemid DNA from the variant clones can be cleaved with the type IIs restriction enzyme and religated to yield the indicated number of recombinant clones, within the limits of the cloning efficiency. If one starts with a subpopulation of preenriched variants from the primary library (say 4×10⁴ clones) then one-sixteenth of all possible recombinants (10⁸) can be obtained.

The construction of “extension libraries” is shown below the dotted line. In this case a project-specific-cassette containing a biased codon distribution encoding some sequence elements previously defined as advantageous for binding to the target is inserted into the hypervariable sequence at the type IIs restriction cleavage site. The large library thus generated encodes a protein containing three segments (domains B, A and C), whereby the central domain A is encoded by the project-specific cassette, and is bordered by the hypervariable domains B and C.

The formuli for the numbers of variants obtained are made for the protocol in which four separate libraries are constructed.

The right side of the figure illustrates how the variant protein might bind to a target protein. The variants selected from the extension library are expected to have a larger surface of interaction and thus to exhibit stronger and/or more specific binding to the defined target. The target may be a cell, a (partially) purified protein or peptide e.g. enzyme, antibody, hormone or lymphokine, cell receptor or in fact any defined surface or particle suspension, possible coated with one of the aforementioned targets, which is amenable to physical separation, i.e. the wall of a receptacle (tube, tubing, flask, microtiter plate, a planar surface), or a particle (e.g. beads, magnetic beads, or droplets in a two-phase liquid system).

FIG. 5: Driven Directed Cloning (DDC)

This figure illustrates an example of a cloning protocol which has excellent properties for the highly efficient construction of hypervariable libraries and extension libraries, which can be used with the cosmix-plexing7 method. The left side of the figure shows the preparation of the hypervariable cassette to be inserted into the cosmid-phagemid double-stranded vector. The cosmid-phagemid vector containing a “stuffer fragment” is shown on the right. Both the PCR-product containing the hypervariable sequence, shown as a line of asterisks, and the vector containing the “stuffer” are cleaved with the same type IIs restriction enzyme(s). It is noted that the recognition sites for this(these) enzyme(s) are oriented in opposite directions, i.e. outwards from the stuffer in the case of the vector, and inwards in the case of the PCR-product. After cleavage neither the hypervariable cassette to be inserted nor the vector contain any of the original type IIs restriction enzyme recognition sites. The vectors and insert are, however designed to have non-palindromic cohesive ends, at their termini, generated by the restriction enzyme cleavage, so that a ligation of insert and vector leads to an oriented insertion of the hypervariable region. In addition, the vector cannot undergo ring closure in the absence of the insert cassette nor can the insert fragments ligate to one another. Since the ligation is carried out at high DNA concentration and in the continued presence of the restriction enzyme any ligation product resembling the in initial uncleaved or partially cleaved vector or PCR-product will be immediately recleaved. This combination of oriented non-palindromic cohesive ends and recleavage of unwanted ligation products, drives, especially at high DNA concentration, where the formation of ring closure of a vector-insert-hybrid is at a disadvantage, the formation of oriented double-stranded concatemers of the structure required for highly efficient cosmid packaging. The primary cosmix-plexing library is formed finally by transducing the packaged cosmid-phagemid hybrids into an E. coli host which contains, or is superinfected with, an M13-like helper phage. The phagemid are repassaged in a second M13 phage-packaging step before use in selection so that individual phage clones are derived from singly infected cells. This is necessary in order that each phagemid particle carries the variant encoded in its genome. This is not the situation in the first packaging step in which the E. coli host contains a concatemer of some eight different variant phagemid.

Recombination can be acheived within the hypervariable region of the gene encoding the protein or peptide presented on the phagemid according to the scheme illustrated in FIG. 1. With extension libraries, either the left (5′) or right (3′) extension, or both, can be reasserted by cleaving with a type IIs restriction enzyme recognizing a site bordering either left end, the right end (opposite orientation), or both ends respectively, as described for the sequences B₁-B_(n) and Q_(n+a+1) . . . Q_(n+a+i) in claim 3.

The use of hypervariable sequences in the description of the invention implies in general that we try to use set of oligonucleotides in which “randomized sequences” encode amino-acids at ratios near to that normally found in natural proteins, whereby the frequency of stop-codons is reduced. We are aware that for certain applications biased subsets may be preferable in the construction of dedicated sublibraries.

FIG. 6 The diagram in FIG. 6A shows a diagram of the phagemid pROCOS4/7. FIG. 6B through FIG. 6E shows the sequence of the phagemid pROCOS4/7 (SEQ ID NO: 17).

FIG. 7 The diagram in FIG. 7A shows a diagram of the phagemid pROCOS5/3. FIG. 7B through FIG. 7E shows the sequence of the phagemid pROCOS5/3 (SEQ ID NO: 18).

EXAMPLE 1 Cosmixplexing Using the Four-tube-method (according to claims 1-10)

1a) Library Generation

Oligonucleotide Sequences:

NONA-CA (SEQ ID NO: 1)

5′ TCGG GGTACC TGGAGCA(XNN)₄KKN(XNN)₄GCTGCACGG         KpnI GAGCTC GCC 3′  SacI

NONA-CT (SEQ ID NO: 2)

5′ TCGGGGTACCTGGAGCA(XNN)₄RRN(XNN)₄GCTGCACGGGAGCTCGCC 3′

NONA-GA (SEQ ID NO: 3)

5′ TCGGGGTACCTGGAGCA(XNN)₄YYN(XNN)₄GCTGCACGGGAGCTCGCC 3′

NONA-GT (SEQ ID NO: 4)

5′ TCGGGGTACCTGGAGCA(XNN)₄MMN(XNN)₄GCTGCACGGGAGCTCGCC 3′

where X means: A, C and G; N: A, C, G and T; K: G and T; R:G and A; Y: C and T; M: C and A.

NONA PCR-L (SEQ ID NO: 5)

5′ GGCGAGCTCCCGTGCAGC 3′

NONA PCR-R (SEQ ID NO: 6)

5′ TCGGGGTACCTGGAGCA 3′

KpnI (GGTACC) and SacI (GAGCTC) restriction enzyme recognition sites are marked in bold type.

Important Vector DNA-Sequences: pROCOS4/7 (SEQ ID NO: 7)

                      Eco47III        SacI     BsqI        KpnI  5′ GGCGAGCTCCCGTGCAGCGCTCCAGGTACCCCGATATCAGAGCT                        BpmI  |pIII→ GAA 3′

pROCOS4/7-Stufferl (SEQ ID NOS: 8,9)

                   Eco47III     Eco47III        SacI    BsgI                        KpnI |pIII→ 5′ GGCGAGCTCCCGTGCAGC GCT...  ...AGCGCTCCAGGTACCCCGATATCAGAGCTGAA 3′                                     BpmI                                                 952 bp Eco47III fragment                     of plasmid pBR322

KpnI (GGTACC), SacI (GAGCTC), BsgI (GTGCAG), Eco47III (AGCGCT) and BpmI (CTGGAG) restriction enzyme recognition sites are marked in bold type. The first codon of the mature pIII protein (GAA) is indicated.

For the generation of double-stranded DNA inserts the single-stranded hypervariable DNA oligos NONA-CA, NONA-CT, NONA-GA and NONA-GT are amplified using the single stranded DNA oligos NONA PCR-L and NONA PCR-R as PCR-primers according to the following protocol:

Remark: the four hypervariable DNA-oligos have to be kept strictly separated!

PCR-Amplification of DNA Oligos

PCR-buffer (10X):

KCl 500 mM Tris-HCl (pH 9.0) 100 mM Triton X-100 1%

Taq DNA polymerase (Promega) in storage buffer A:

glycerol 50% Tris-HCl (pH 8.0) 50 mM NaCl 100 mM EDTA 0.1 mM DTT 1 mM Triton X-100 1% TE-buffer (1X) Tris-HCl (pH 8.0) 10 mM EDTA 0.1 mM

1. Transfer 2 μl of a 10 pmol/μl solution of the hypervariable oligos NONA-CA, -CT, -GA and -GT in a 0.2 ml PCR reaction tube (4 tubes).

2. Mix the following in one Eppendorf reaction tube:

ddH₂O 276.75 μl PCR-buffer (10X) 45.0 μl NONA PCR-L (100 pmol/μl) 9.0 μl NONA PCR-R (100 pmol/μl) 9.0 μl dNTPs (10 mM each) 9.0 μl Taq DNA polymerase (5 U/μl) 2.25 μl

3. Transfer 78 μl of this mixture to each of the PCR tubes containing the hypervariable oligos (step 1).

4. Mix 45 μl MgCl₂ (25 mM) and 45 μl ddH₂O in an Eppendorf reaction tube.

5. Preheat a PCR thermocycler to 94° C. (if possible use a heated lid).

6. Transfer 20 μl of the MgCl₂ solution (step 4) into each of the PCR tubes (step 3).

7. Put the tubes directly into the thermocycler (simplified hot-start) and run the following program:

1. 94° C. 30 sec 2. 94° C. 10 sec 3. 52° C. 10 sec 4. repeat 9 times step 2 and 3 5. hold at 4° C.

8. Take an aiquot of 5 μl to run a 4.5% agarose gel.

9. Add 200 μl ddH₂O to each tube, extract with phenol, precipitate with ethanol and resuspend the DNA in 120 μl TE-buffer.

For cloning the amplified oligo-DNA are cut with KpnI and SacI. Also the vector-DNA has to be cut with both enzymes. As vector-DNA pROCOS4/7 or a derivative thereof named pROCOS4/7-Stuffer1 which contains a DNA-Stuffer fragment for easier control of the double digest reaction can be used without any consequences regarding the final cloning results. Digestions are done according to the following protocols:

buffer B + TX-100 (1X) Tris-HCl (pH 7.5) 10 mM MgCl2 10 mM BSA 0.1 mg/ml Triton X-100 0.02% buffer A (1X) Tris-acetate (pH 7.9) 33 mM Mg-acetate 10 mM K-acetate 66 mM Dithiothreitol 0.5 mM

Vector DNA Digestion

1. For the restriction digestion of the vector DNA with KpnI set up the following mixture:

pROCOS4/7-Stuffer1 X μl (200 μg) buffer B + TX-100 (10X) 150 μl BSA (10 mg/ml = 100X) 15 μl KpnI X μl (400 U) ddH₂O to 1500 μl

incubate at 37° C. for 3 hr and stop the reaction by incubating at 65° C. for 20 min.

2. Take an aliquot of 3 μl and run a 1% agarose gel with uncleaved DNA as a control.

3. Extract with phenol, precipitate with ethanol and resuspend the DNA in 820 μl TE-buffer.

4. Store a 20 μl aliquot of the digested DNA at −20° C. and mix the following for the digestion with SacI:

pROCOS4/7-Stuffer/KpnI 800 μl buffer A (10X) 100 μl SacI X μl (400 U) ddH₂O 1000 μl

incubate at 37° C. for 3 hr.

5. Take an aliquot of 3 μl and run a 1% agarose gel using uncleaved and single-cut DNA as a control.

6. Extract with phenol, precipitate with ethanol and resuspend the DNA in 550 μl TE-buffer.

Oligo DNA Digestion

1. For the digestion of double-stranded (ds) oligo DNA with KpnI set up the following four mixtures:

NONA—CA, —CT, —GA or —GT dsDNA 100 μl buffer B + TX-100 (10X) 50 μl BSA (10 mg/ml = 100X) 5 μl KpnI X μl (400 U) ddH₂O to 500 μl

incubate at 37° C. for 5 hr.

NOTE: Don't heat up the oligo DNA.

2. Take an aliquot of 5 μl and run an 4.5% agarose gel with uncleaved DNA as a control.

3. Extract with phenol, precipitate with ethanol and resuspend the DNA in 110 μl TE-buffer.

4. Store an 10 μl aliquot of the digested DNA at −20° C. and set up the following four mixtures for the digestion with SacI:

NONA—CA, —CT, —GA or —GT/KpnI 100 μl buffer A (10X) 50 μl SacI X μl (400 U) ddH₂O to 500 μl

incubate at 37° C. for 5 hr.

5. Take an aliquot of 5 μl and run an 4.5% agarose gel using uncleaved and single-cut DNA as a control.

6. Extract with phenol, precipitate with ethanol and resuspend the DNA in 55 μl TE-buffer.

The vector-DNA fragment may be purified using the following protocol:

Purification of Vector DNA Fragments by Gel Extraction

1. To separate the pROCOS4/7 vector DNA fragment from the stuffer fragment prepare a horizontal 1% agarose gel using a one-tooth combs.

2. Mix the DNA with {fraction (1/10)} vol gel loading buffer, load onto the gel and electrophorese at 100 V until both fragments are clearly separated.

3. Put the gel on the UV transilluminator and excise the 5.5 kb pROCOS4/7 vector DNA fragment.

4. Extract the agarose slice using the JETsorb gel extraction kit (Genomed GmbH, Germany).

Vector- and insert DNA fragments are ligated and transformed according to the following protocols:

Ligation of DNA Fragments

Check the integrity of vector and insert DNA fragments by agarose gel electrophoresis (1% and 4.5% respectively). The concentration of the insert DNA may be estimated by comparing its ethidium bromide staining with standards of known quantity like assembled oligonucleotides. To determine the vector DNA concentration determine the absorbance at 260/280 nm.

T4 DNA ligase buffer (1X):

Tris-HCl (pH 7.5) 50 mM MgCl₂ 10 mM Dithiotreitol 10 mM ATP 1 mM BSA 25 μg/ml

Test Ligation

1. To determine the appropriate ratio of insert to vector DNA a series of test ligations may be performed. For this assemble ligation reactions composed of:

vector DNA fragment X μl (0.5 μg) T4 DNA ligase buffer (10X) 1 μl ddH₂O to 9 μl

2. Prepare three twofold dilutions of the insert DNA's in ddH₂O and add 1 μl of undiluted DNA as well as 1 μl of each dilution to one of the ligations reactions.

NOTE: The aim of this is to create vector to insert DNA (V/I) ratios of 1:5 to 2:1.

3. Add 1 unit T4 DNA ligase to each reaction and incubate overnight at 15° C.

NOTE: As a control one reaction without insert DNA and one without ligase should be included.

4. Add 1 vol ddH₂O to each reaction and incubate at 65° C. for 10 min.

5. Precipitate the DNA with ethanol and resuspend it in 10 μl TE buffer.

6. Transform electrocompetent E. coli JM110λ cells with the content of each tube and plate dilutions on ampicillin containing LB agar plates.

Large-Scale Ligation

1. To create the libraries set up four of the following mixtures:

vector DNA fragment X μl (¼ of the total prep.) insert DNA X μl (to create the optimal V/I- ratio) T4 DNA ligase buffer (10X) X μl ({fraction (1/10)} of the final vol) T4 DNA ligase X μl (2 U/μg DNA) ddH₂O to create a DNA conc. of 0.05 μg/μl

2. Extract with phenol, precipitate with ethanol and resuspend each of the ligation mixtures in sufficient TE-buffer to adjust the DNA concentration to 0.1-0.2 μg/μl.

Preparation of Competent Cells

1. Inoculate 20 ml of LB medium with a single colony of E. coli JM110λ and incubate at 37° C. and 180 rpm overnight.

2. Next day inoculate 2×1 liter of LB medium (2×21 Erlenmeyer flask) at 1% with the overnight grown culture and incubate again at same conditions until an optical density of OD₆₀₀=0.6 has been reached.

3. Transfer 250 ml aliquots of the culture into centrifuge tubes (GS3), chill the cells on ice and centrifuge for 15 min at 8000 rpm and 4° C. (Sorvall RC5C centrifuge; GS3 rotor). Decant the supernatant.

4. Resuspend each pellet in 250 ml of ice-cold ddH₂O, centrifuge again (step 3) and decant the supernatant.

5. Resuspend each pellet in 125 ml of ice-cold ddH₂O, collect each of two aliquots in one tube, centrifuge again (step 3) and decant the supernatant.

6. Resuspend each pellet in 10 ml of ice-cold sterile glycerol (10%), collect all of the aliquots in one GSA centrifuge tube, centrifuge for 15 min at 8000 rpm and aspirate the supernatant.

7. Resuspend the bacterial pellet in 10 ml of ice-cold sterile glycerol (10%).

8. Fill aliquots of 100 μl in precooled, sterile Eppendorf reaction tubes, freeze immediately in liquid nitrogen and store at −70° C.

Transformation of E. coli Cells by Electroporation

1. Place freezed aliquots of competent E. coli cells on ice and let them thaw.

2. To each aliquot add up to 2 μg DNA in less than 10 μl and incubate on ice for 1 minute.

3. Fill the suspension in a prechilled electroporation cuvette (0.2 cm pathlength), place the cuvette in the electroporation sled and give a pulse at a voltage of 2.5 kV, a capacity of 25 μF and a resistence of 200 Ω (Gene Pulser and Puls Controller, Bio-Rad).

4. Immediately add 1 ml of LB medium (supplemented with 20 mM Glucose), mix and transfer the suspension in an Eppendorf reaction tube.

5. Incubate for 1 hour at 37° C. and plate on LB agar plates containing ampicillin (100 μg/ml). Incubate overnight at 37° C.

NOTE: To determine the size of the libraries also plate dilutions of the transformed cells.

6. To create library stocks resuspend the cells in LB/ampicillin medium, mix with 1 vol of sterile 87% glycerol and store at −70° C.

1b) Recombination

For recombination within the hypervariable Sequences according to the four tube cosmixplexing method the libraries can be preselected. For this purpose the E. coli cells containing the phagemid libraries are superinfected with M13K07 helperphages, progeny phages presenting fusionproteins are harvested and used for the first round of a panning according to standard methods e.g.:

Preparation of M13K07 Phage Stocks

PEG/NaCl-solution:

(16.7% /3.3 M)

100 g PEG 8000

116.9 g NaCl

475 ml H₂O

PBS-buffer (1×):

8.0 g NaCl

0.2 g KCl

1.43 g Na₂HPO₄ +2 H₂O

0.2 g KH₂PO₄

H₂O ad 11

pH 6.8-7

1. Use a disposable pasteur pipette to pick a single, well separated M13K07 μlaque from a E. coli WK6 lawn grown overnight on a LB/kanamycin (Km) plate, inoculate 20 ml of LB(2×)/Km medium (100 ml Erlenmeyer flask) with this agar slice and incubate overday at 37° C. on a shaker at 180 rpm.

2. Inoculate 2×500 ml LB(2×)/Km medium (in 2 l Erlenmeyer flasks) with 10 ml preculture and incubate overnight (37° C., 180 rpm).

3. Next day centrifuge four 250 ml aliquots for 15 minutes at 8,000 rpm and 4° C. (Sorvall RC5C centrifuge; GS3 rotor). Transfer the supernatant into centrifuge bottles, centrifuge and transfer the supernatant again into fresh centrifuge bottles.

4. Add 0.15 vol. of PEG/NaCl solution, mix and incubate on ice for at least 2 hours.

5. Centrifuge for 60 min at 8000 rpm (GS3 rotor), decant the supernatant, centrifuge for some sec at up to 4000 rpm and remove last traces of the supernatant using a pipette.

6. Resuspend each PEG-pellet in 2.5 ml PBS solution and collect the resuspended phages in one SS34 centrifuge bottle. To clear the suspension centrifuge again for 10 min at 12000 rpm (SS34 rotor). Recover the supernatant (pipette), add NaN₃ to a final concentration of 0.02% and store the phages at 4° C.

Packaging of Phagemids (keep each library separate!)

1. Inoculate 100 ml of LB/Amp medium (1 l Erlenmeyer flask) with 1 ml of E. coli JM110λ cells containing phagemids (from overnight culture or resuspended cells) and incubate at 37° C. and 180 rpm until OD₆₀₀=0.5 (2.5 h).

2. Add 500 μl M13K07 stock solution (1011-1012 cfu/ml), incubate at 37° C. for 15 min and continue shaking at 37° C. and 180 rpm overnight.

3. Next day centrifuge for 10 min at 8000 rpm (GSA rotor), decant the supernatant into a fresh bottle and repeat the centrifugation step.

4. Add 0.15 Vol of PEG/NaCl solution and incubate on ice for at least two hours.

5. Centrifuge for 60 min at 10000 rpm (GSA rotor), decant the supernatant and repeat the centrifugation and remove the supernatant completely.

6. Dissolve the pellet in 1 ml of PBS buffer and transfer the solution into an Eppendorf reaction tube. Centrifuge for 10 min at 13000 rpm (batch centrifuge), recover the cleared solution and add NaN₃ (final concentration of 0.02%). Store at 4° C.

Panning Procedure (keep each library separate!)

T-PBS Solution:

PBS-buffer containing 0.5% Tween 20

Blocking Solution:

PBS-buffer containing 2% skim milk powder

Elution-buffer:

glycine (0.1 M; pH 2.2)

1. Coating of Microtiter Plates:

Fill 100 μl of ligand solution (100 μg/ml PBS) into the wells of a 96-well microtiter plate (Nunc maxisorb) and incubate overnight at 4° C. or at least 2 hours at room temperature. Shake out the wells, slap the plate onto a paper towel and wash the wells once with T-PBS solution (ELISA plate washer or manually).

2. Blocking:

Fill the wells with 400 μl of blocking solution and incubate at room temperature for ˜1 hour. Shake out the wells, slap the plate onto a paper towel and wash the wells once with T-PBS.

3. Binding:

Fill the coated and one uncoated well (as a control) with 100 μl of phage preparations diluted 1:1 with skim milk powder (usually 10¹⁰-10¹¹ phages/well) and incubate at room temperature for 1 to 3 hours.

4. Washing:

Remove the Solutions Using a Pipette and Slap the Plate Onto a Paper Towel.

In the first round of panning wash the wells once with T-PBS, incubate for 10 min with 400 μl blocking solution, wash again with T-PBS and finally two times with water. During all further rounds repeat the T-PBS washing steps three times. All washing steps can be carried out manually using a pipette or with an ELISA plate washer.

5. Elution:

Slap out the plate and fill the wells with 100 μl of elution-buffer, incubate at room temperature for 15 min and transfer the solution into an Eppendorf reaction tube containing 6 μl Tris (2 M).

6. Determine the Titer of Eluted Phages as Described Under 3.1.3.

Reinfection of E. coli Cells (keep each library separate!)

1. Mix the eluted phages and 10 ml of E. coli JM110λ log-phase cells and incubate for 30 min at 37° C.

2. Collect the cells by centrifugation (5 min, 8000 rpm, SS34 rotor) and resuspend the pellet in 400 μl of LB/Amp medium.

3. Plate each suspension on one LB/Amp agar plate (Ø14.5 cm) and incubate overnight at 37° C.

After one round of panning populations of about 10⁵ individual clones enriched towards binding one's are expected. For recombination the phagemid DNA has to isolated according to standard protocols, e.g.:

Preparation of Phagemid-DNA from Reinfected Cells

1. Resuspend reinfected E. coli cells in 20 ml of LB/Amp medium and use 200 μl for the inoculation of 3 ml LB/Amp medium.

2. Incubate at 180 rpm and 37° C. for 1 hour.

3. Prepare the DNA using Jetquick Plasmid Miniprep Spin Kits (Genomed GmbH, Germany) according to the instructions of the supplier.

Using this method up to 30 pg of DNA can be isolated. For pROCOS4/7 based libraries the phagemid size is 4.3 kb corresponding to a molecular weight of 2.9×10⁶ g/mol or round about 2×10¹¹ phagemid molecules/μg DNA. Therefore 10 μg of recombined DNA contains more molecules than the theoretical number of different variants that can be created from 10⁵ clones (10⁵)²=10¹⁰).

For recombination the phagemid DNA of each preselected library is cut separately e.g. with BpmI or alternatively with BsgI:

Digestion of the Phagemid DNA

NEB3-buffer (1X) NaCl 100 mM Tris-HCl (pH 7.9) 50 mM MgCl₂ 10 mM Dithiothreitol 1 mM

1. Set up the following reaction

phagemid-DNA 10 μg BpmI (2 u/μl) 5 μl NEB3 (10X) 4 μl BSA (1 mg/ml) 4 μl H₂O up to 40 μl incubate at 37° C. for 5 hr.

2. Take an aliquots of 4 μl and run a 1% agarose gel to check the digestion.

3. Extract with phenol, precipitate with ethanol and resuspend the DNA in TE-buffer.

Digested phagemid-DNA's are religated at high concentration (≧0.2 μg/μl) to favour formation of concatemers, packaged into λ phage particles and used for the transfection of E. coli cells (according to “Packaging of Bacteriophage λ DNA in vitro; protocol I” p.2.100-2.104, in: Molecular Cloning- a Laboratory Manual, Sambroock et al. (eds.), 2. ed., 1989, Cold Spring Harbour Laboratory Press). Transfected phagemids are separated by packaging reinfection using M13K07 helperphages (see above).

EXAMPLE 2 Cosmixplexing Using the One-tube-method (according to claims 11-17 and 44)

2a) Library Generation

Oligonucleotide sequences:

NONACOS-NGG (SEQ ID NO: 10)

              BpiI  Bsg I 5′ GGCTCTGATGGAAGACGT↓GCAG C(NNB)₄NGG(NNB)₄TG C↓TCCAG A GTCTTC CTCCTGTCG 3′                         |                   BpmI ↑ BpiI

NONACOS-NCT (SEQ ID NO: 12)

5′ GGCTCTGATGGAAGACGTGCAGC(NNB)₄NCT(NNB)₄TGCTCCAGAGTCTTCCTCCTGTCG 3′

NONACOS-NAM (SEQ ID NO: 12)

5′ GGCTCTGATGGAAGACGTGCAGC(NNB)₄NAM(NNB)₄TGCTCCAGAGTCTTCCTCCTGTCG 3′

NONACOS-NTS (SEQ ID NO: 13)

5′ GGCTCTGATGGAAGACGTGCAGC(NNB)₄NTS(NNB)₄TGCTCCAGAGTCTTCCTCCTGTCG 3′

where N means: A, C, G or T; B: C, G or T; M: A or C and S: C, G or T.

NONACOS-PCR-L (SEQ ID NO: 14)

               BpiI  BsgI 5′ GGCTCTGATGGAAGACGTGCAG 3′

NONACOS-PCR-R (SEQ ID NO: 15)

              BpiI BpmI  5′ CGACAGGAGGAAGACTCTGGAG 3′

BpiI (GAAGAC), BsgI (GTGCAG) and BpmI (CTCCAG) restriction enzyme recognition sites are marked in bold type. BpiI cutting sites are marked by arrows.

Important Vector DNA-sequences of pROCOS5/3 (SEQ ID NO: 16)

               BsqI         Eco47III 5′ GGCGAGCTCCCGT↓GCAG CG GTCTTCAGCGCTTGCCGTCTGACCGT                      ↑  BpiI         Eco47III  BpiI           AGCGCTGGAAGACG C↓TCCAG AGGGTACCCCGATATCAG                         BpmI ↑      |pIII→ AGCTGAA 3′

BpiI (GAAGAC), BsgI (GTGCAG) Eco47III (AGCGCT) and BpmI (CTCCAG) restriction enzyme recognition sites are marked in bold type. BpiI cutting sites are marked by arrows. The first codon of the mature pIII-Protein (GAA) is also indicated.

To create libraries according to the one-tube method the hypervariable oligos NONACOS-NGG, -NCT, -NAM and -NTS are amplified using the PCR-primer NONACOS-R and NONACOS-L as described in example 1, except that the oligo-DNA's don't have to be kept separate.

After this pROCOS5/3-vector-DNA and double stranded (ds) oligo-DNA are digested with BpiI and ligated at the same time according to the following Protocol:

Digestion/Ligation

1. Set up the following mixture:

pROCOS5/3 DNA 200 μg NONACOS—NGG, —NCT, —NAM and —NTS ds DNA 100 μl BpiI 200 u buffer G (10x) 40 μl BSA (10 mg/ml) 4 μl H₂O up to 400 μl

incubate at 37° C. for 2 hr, add 200 units T4 DNA ligase and continue the incubation at 15 to 30° C. over night.

2. Take an aliquot of 3 μl and run an 1% agarose gel as a control.

This protocol favours the production of concatemers of the desired product, that can be packaged for example in E. coli JM110λ cells by λ-packaging according to example 1.

2b) Recombination

For panning and recombination the same methods as described for example 1 can be used, except that one library is used instead of four separate libraries.

LIST OF REFERENCE NUMERALS

FIG. 1.

1 Phagemid library in vitro

2 1. Type IIs restriction and ligation 2. In vitro packaging in a lamda packaging mix 3. Transduction into E. coli

Efficiency≧10⁷/microgram ligated DNA

3 cosmid containing a concatamer of phagemid

4 Superinfection by M13K07

5 ca. 7 to 8 different phagemid are released per E. coli clone Total efficiency≧10⁸/microgram ligated DNA

6 Phagemid particles each presenting different variant proteins

FIG. 2.

1 Enzyme A(type IIS) cleavage and ligation to concatamers

2 In vitro lambda packaging+transduction in E. coli

3 M13-helper phage superinfection (repackaging of individual phagemid from the concatenate)

4 What one puts in is what one gets out.

FIG. 3.

1 M13 replication/packaging origin=type IIs enzyme A cleavage site

2 Enzyme A+B (type IIs) cleavage and ligation to concatamers

3 In vitro lambda packaging+transduction in E. coli

4 M13-helper phage superinfection (repackaging of individual phagemid from the concatenate)

5 The left and right of the type IIs cleavage site B are recombined.

FIG. 4.

Cosmix-plexing® Strategies

1 Reassortment after cleavage and repackaging

2 project-specific cassette

3 Reassortment after cleavage and repackaging

4 target

5 panning selection with a standard cosmix-plexing® library

6 primary selected ligand (domain A)

7 panning selection with a cosmix-plexing® inserting the consensus cassette from the initial library into an extension library

8 secondary optimized ligand selected from an extension library (domains B, A+C; B+C from the extensions)

9 continue optimization?

1. reassort, left and or right extension

2. insert another cassette→reinsert central cassettes in new extension library

3. repeat any steps . . . .

FIG. 5.

Driven Directed Cloning (DDC) for the Construction of Primary Libraries

1 hypervariable region

2 type IIs restriction enzyme cleavage

3 Ligation in the presence of restriction enzyme

4 “stuffer”

5 Cosmid packaging and phagemid packaging +M13-type helper phage

6 hybrid phagemid

18 62 base pairs nucleic acid single linear other nucleic acid /desc = “hypervariable DNA oligo” not provided misc_feature 18 /note= “V = A or C or G” misc_feature 21 /note= “V = A or C or G” misc_feature 19 /note= “N can be A, C, G or T” misc_feature 20 /note= “N can be A, C, G or T” misc_feature 22 /note= “N can be A, C, G or T” misc_feature 23 /note= “N can be A, C, G or T” misc_feature 24 /note= “V = A or C or G” misc_feature 25 /note= “N can be A, C, G or T” misc_feature 26 /note= “N can be A, C, G or T” misc_feature 27 /note= “V = A or C or G” misc_feature 28 /note= “N can be A, C, G or T” misc_feature 29 /note= “N can be A, C, G or T” misc_feature 30 /note= “K can be G or T” misc_feature 31 /note= “K can be G or T” misc_feature 32 /note= “N can be A, C, G or T” misc_feature 33 /note= “V = A or C or G” misc_feature 34 /note= “N can be A, C, G or T” misc_feature 35 /note= “N can be A, C, G or T” misc_feature 36 /note= “V = A or C or G” misc_feature 37 /note= “N can be A, C, G or T” misc_feature 38 /note= “N can be A, C, G or T” misc_feature 39 /note= “V = A or C or G” misc_feature 40 /note= “N can be A, C, G or T” misc_feature 41 /note= “N can be A, C, G or T” misc_feature 42 /note= “V = A or C or G” misc_feature 43 /note= “N can be A, C, G or T” misc_feature 44 /note= “N can be A, C, G or T” 1 TCGGGGTACC TGGAGCAVNN VNNVNNVNNK KNVNNVNNVN NVNNGCTGCA CGGGAGCTCG 60 CC 62 62 base pairs nucleic acid single linear other nucleic acid /desc = “hypervariable DNA oligo” not provided misc_feature 18 /note= “V = A or C or G” misc_feature 19 /note= “N can be A, C, G or T” misc_feature 20 /note= “N can be A, C, G or T” misc_feature 21 /note= “V = A or C or G” misc_feature 22 /note= “N can be A, C, G or T” misc_feature 23 /note= “N can be A, C, G or T” misc_feature 24 /note= “V = A or C or G” misc_feature 25 /note= “N can be A, C, G or T” misc_feature 26 /note= “N can be A, C, G or T” misc_feature 27 /note= “V = A or C or G” misc_feature 28 /note= “N can be A, C, G or T” misc_feature 29 /note= “N can be A, C, G or T” misc_feature 30 /note= “R can be G or A” misc_feature 31 /note= “R can be G or A” misc_feature 32 /note= “N can be A, C, G or T” misc_feature 33 /note= “V = A or C or G” misc_feature 34 /note= “N can be A, C, G or T” misc_feature 35 /note= “N can be A, C, G or T” misc_feature 36 /note= “V = A or C or G” misc_feature 37 /note= “N can be A, C, G or T” misc_feature 38 /note= “N can be A, C, G or T” misc_feature 39 /note= “V = A or C or G” misc_feature 40 /note= “N can be A, C, G or T” misc_feature 41 /note= “N can be A, C, G or T” misc_feature 42 /note= “V = A or C or G” misc_feature 43 /note= “N can be A, C, G or T” misc_feature 44 /note= “N can be A, C, G or T” 2 TCGGGGTACC TGGAGCAVNN VNNVNNVNNR RNVNNVNNVN NVNNGCTGCA CGGGAGCTCG 60 CC 62 62 base pairs nucleic acid single linear other nucleic acid /desc = “hypervariable DNA oligo” not provided misc_feature 18 /note= “V = A or C or G” misc_feature 19 /note= “N can be A, C, G or T” misc_feature 20 /note= “N can be A, C, G or T” misc_feature 21 /note= “V = A or C or G” misc_feature 22 /note= “N can be A, C, G or T” misc_feature 23 /note= “N can be A, C, G or T” misc_feature 24 /note= “V = A or C or G” misc_feature 25 /note= “N can be A, C, G or T” misc_feature 26 /note= “N can be A, C, G or T” misc_feature 27 /note= “V = A or C or G” misc_feature 28 /note= “N can be A, C, G or T” misc_feature 29 /note= “N can be A, C, G or T” misc_feature 30 /note= “Y = C or T” misc_feature 31 /note= “Y = C or T” misc_feature 32 /note= “N can be A, C, G or T” misc_feature 33 /note= “V = A or C or G” misc_feature 34 /note= “N can be A, C, G or T” misc_feature 35 /note= “N can be A, C, G or T” misc_feature 36 /note= “V = A or C or G” misc_feature 37 /note= “N can be A, C, G or T” misc_feature 38 /note= “N can be A, C, G or T” misc_feature 39 /note= “V = A or C or G” misc_feature 40 /note= “N can be A, C, G or T” misc_feature 41 /note= “N can be A, C, G or T” misc_feature 42 /note= “V = A or C or G” misc_feature 43 /note= “N can be A, C, G or T” misc_feature 44 /note= “N can be A, C, G or T” 3 TCGGGGTACC TGGAGCAVNN VNNVNNVNNY YNVNNVNNVN NVNNGCTGCA CGGGAGCTCG 60 CC 62 62 base pairs nucleic acid single linear other nucleic acid /desc = “hypervariable DNA oligo” not provided misc_feature 18 /note= “V = A or C or G” misc_feature 19 /note= “N can be A, C, G or T” misc_feature 20 /note= “N can be A, C, G or T” misc_feature 21 /note= “V = A or C or G” misc_feature 22 /note= “N can be A, C, G or T” misc_feature 23 /note= “N can be A, C, G or T” misc_feature 24 /note= “V = A or C or G” misc_feature 25 /note= “N can be A, C, G or T” misc_feature 26 /note= “N can be A, C, G or T” misc_feature 27 /note= “V = A or C or G” misc_feature 28 /note= “N can be A, C, G or T” misc_feature 29 /note= “N can be A, C, G or T” misc_feature 30 /note= “M = A or C” misc_feature 31 /note= “M = A or C” misc_feature 32 /note= “N can be A, C, G or T” misc_feature 33 /note= “V = A or C or G” misc_feature 34 /note= “N can be A, C, G or T” misc_feature 35 /note= “N can be A, C, G or T” misc_feature 36 /note= “V = A or C or G” misc_feature 37 /note= “N can be A, C, G or T” misc_feature 38 /note= “N can be A, C, G or T” misc_feature 39 /note= “V = A or C or G” misc_feature 40 /note= “N can be A, C, G or T” misc_feature 41 /note= “N can be A, C, G or T” misc_feature 42 /note= “V = A or C or G” misc_feature 43 /note= “N can be A, C, G or T” misc_feature 44 /note= “N can be A, C, G or T” 4 TCGGGGTACC TGGAGCAVNN VNNVNNVNNM MNVNNVNNVN NVNNGCTGCA CGGGAGCTCG 60 CC 62 18 base pairs nucleic acid single linear other nucleic acid /desc = “DNA oligo” not provided 5 GGCGAGCTCC CGTGCAGC 18 17 base pairs nucleic acid single linear other nucleic acid /desc = “DNA oligo” not provided 6 TCGGGGTACC TGGAGCA 17 47 base pairs nucleic acid single linear other nucleic acid /desc = “vector DNA-Sequence” not provided 7 GGCGAGCTCC CGTGCAGCGC TCCAGGTACC CCGATATCAG AGCTGAA 47 21 base pairs nucleic acid single linear other nucleic acid /desc = “pROCOS4/7-Stuffer 1” not provided 8 GGCGAGCTCC CGTGCAGCGC T 21 32 base pairs nucleic acid single linear other nucleic acid /desc = “ pROCOS4/7-Stuffer 1” not provided 9 AGCGCTCCAG GTACCCCGAT ATCAGAGCTG AA 32 74 base pairs nucleic acid single linear other nucleic acid /desc = “hypervariable DNA oligo” not provided misc_feature 24 /note= “N = A or C or G or T” misc_feature 25 /note= “N = A or C or G or T” misc_feature 26 /note= “B = C or G or T” misc_feature 27 /note= “N = A or C or G or T” misc_feature 28 /note= “N = A or C or G or T” misc_feature 29 /note= “B = C or G or T” misc_feature 30 /note= “N = A or C or G or T” misc_feature 31 /note= “N = A or C or G or T” misc_feature 32 /note= “B = C or G or T” misc_feature 33 /note= “N = A or C or G or T” misc_feature 34 /note= “N = A or C or G or T” misc_feature 35 /note= “B = C or G or T” misc_feature 36 /note= “N = A or C or G or T” misc_feature 39 /note= “N = A or C or G or T” misc_feature 40 /note= “N = A or C or G or T” misc_feature 41 /note= “B = C or G or T” misc_feature 42 /note= “N = A or C or G or T” misc_feature 43 /note= “N = A or C or G or T” misc_feature 44 /note= “B = C or G or T” misc_feature 45 /note= “N = A or C or G or T” misc_feature 46 /note= “N = A or C or G or T” misc_feature 47 /note= “B = C or G or T” misc_feature 48 /note= “N = A or C or G or T” misc_feature 49 /note= “N = A or C or G or T” misc_feature 50 /note= “B = C or G or T” 10 GGCTCTGATG GAAGACGTGC AGCNNBNNBN NBNNBNGGNN BNNBNNBNNB TGCTCCAGAG 60 TCTTCCTCCT GTCG 74 74 base pairs nucleic acid single linear other nucleic acid /desc = “hypervariable DNA oligo” not provided misc_feature 24 /note= “N = A or C or G or T” misc_feature 25 /note= “N = A or C or G or T” misc_feature 26 /note= “B = C or G or T” misc_feature 27 /note= “N = A or C or G or T” misc_feature 28 /note= “N = A or C or G or T” misc_feature 29 /note= “B = C or G or T” misc_feature 30 /note= “N = A or C or G or T” misc_feature 31 /note= “N = A or C or G or T” misc_feature 32 /note= “B = C or G or T” misc_feature 33 /note= “N = A or C or G or T” misc_feature 34 /note= “N = A or C or G or T” misc_feature 35 /note= “B = C or G or T” misc_feature 36 /note= “N = A or C or G or T” misc_feature 39 /note= “N = A or C or G or T” misc_feature 40 /note= “N = A or C or G or T” misc_feature 41 /note= “B = C or G or T” misc_feature 42 /note= “N = A or C or G or T” misc_feature 43 /note= “N = A or C or G or T” misc_feature 44 /note= “B = C or G or T” misc_feature 45 /note= “N = A or C or G or T” misc_feature 46 /note= “N = A or C or G or T” misc_feature 47 /note= “B = C or G or T” misc_feature 48 /note= “N = A or C or G or T” misc_feature 49 /note= “N = A or C or G or T” misc_feature 50 /note= “B = C or G or T” 11 GGCTCTGATG GAAGACGTGC AGCNNBNNBN NBNNBNCTNN BNNBNNBNNB TGCTCCAGAG 60 TCTTCCTCCT GTCG 74 74 base pairs nucleic acid single linear other nucleic acid /desc = “hypervariable DNA oligo” not provided misc_feature 24 /note= “N = A or C or G or T” misc_feature 25 /note= “N = A or C or G or T” misc_feature 26 /note= “B = C or G or T” misc_feature 27 /note= “N = A or C or G or T” misc_feature 28 /note= “N = A or C or G or T” misc_feature 29 /note= “B = C or G or T” misc_feature 30 /note= “N = A or C or G or T” misc_feature 31 /note= “N = A or C or G or T” misc_feature 32 /note= “B = C or G or T” misc_feature 33 /note= “N = A or C or G or T” misc_feature 34 /note= “N = A or C or G or T” misc_feature 35 /note= “B = C or G or T” misc_feature 36 /note= “N = A or C or G or T” misc_feature 38 /note= “M = A or C” misc_feature 39 /note= “N = A or C or G or T” misc_feature 40 /note= “N = A or C or G or T” misc_feature 41 /note= “B = C or G or T” misc_feature 42 /note= “N = A or C or G or T” misc_feature 43 /note= “N = A or C or G or T” misc_feature 44 /note= “B = C or G or T” misc_feature 45 /note= “N = A or C or G or T” misc_feature 46 /note= “N = A or C or G or T” misc_feature 47 /note= “B = C or G or T” misc_feature 48 /note= “N = A or C or G or T” misc_feature 49 /note= “N = A or C or G or T” misc_feature 50 /note= “B = C or G or T” 12 GGCTCTGATG GAAGACGTGC AGCNNBNNBN NBNNBNAMNN BNNBNNBNNB TGCTCCAGAG 60 TCTTCCTCCT GTCG 74 74 base pairs nucleic acid single linear other nucleic acid /desc = “hypervariable DNA oligo” not provided misc_feature 24 /note= “N = A or C or G or T” misc_feature 25 /note= “N = A or C or G or T” misc_feature 26 /note= “B = C or G or T” misc_feature 27 /note= “N = A or C or G or T” misc_feature 28 /note= “N = A or C or G or T” misc_feature 29 /note= “B = C or G or T” misc_feature 30 /note= “N = A or C or G or T” misc_feature 31 /note= “N = A or C or G or T” misc_feature 32 /note= “B = C or G or T” misc_feature 33 /note= “N = A or C or G or T” misc_feature 34 /note= “N = A or C or G or T” misc_feature 35 /note= “B = C or G or T” misc_feature 36 /note= “N = A or C or G or T” misc_feature 38 /note= “B = C or G or T” misc_feature 39 /note= “N = A or C or G or T” misc_feature 40 /note= “N = A or C or G or T” misc_feature 41 /note= “B = C or G or T” misc_feature 42 /note= “N = A or C or G or T” misc_feature 43 /note= “N = A or C or G or T” misc_feature 44 /note= “B = C or G or T” misc_feature 45 /note= “N = A or C or G or T” misc_feature 46 /note= “N = A or C or G or T” misc_feature 47 /note= “B = C or G or T” misc_feature 48 /note= “N = A or C or G or T” misc_feature 49 /note= “N = A or C or G or T” misc_feature 50 /note= “B = C or G or T” 13 GGCTCTGATG GAAGACGTGC AGCNNBNNBN NBNNBNTBNN BNNBNNBNNB TGCTCCAGAG 60 TCTTCCTCCT GTCG 74 22 base pairs nucleic acid single linear other nucleic acid /desc = “DNA primer” not provided 14 GGCTCTGATG GAAGACGTGC AG 22 22 base pairs nucleic acid single linear other nucleic acid /desc = “DNA primer” not provided 15 CGACAGGAGG AAGACTCTGG AG 22 90 base pairs nucleic acid single linear other nucleic acid /desc = “DNA vector” not provided 16 GGCGAGCTCC CGTGCAGCGG TCTTCAGCGC TTGCCGTCTG ACCGTAGCGC TGGAAGACGC 60 TCCAGAGGGT ACCCCGATAT CAGAGCTGAA 90 4614 base pairs nucleic acid single linear DNA (genomic) not provided 17 GGCGAGCTCC CGTGCAGCGC TCCAGGTACC CCGATATCAG AGCTGAAACT GTTGAAAGTT 60 GTTTAGCAAA ATCCCATACA GAAAATTCAT TTACTAACGT CTGGAAAGAC GACAAAACTT 120 TAGATCGTTA CGCTAACTAT GAGGGCTGTC TGTGGAATGC TACAGGCGTT GTAGTTTGTA 180 CTGGTGACGA AACTCAGTGT TACGGTACAT GGGTTCCTAT TGGGCTTGCT ATCCCTGAAA 240 ATGAGGGTGG TGGCTCTGAG GGTGGCGGTT CTGAGGGTGG CGGTTCTGAG GGTGGCGGTA 300 CTAAACCTCC TGAGTACGGT GATACACCTA TTCCGGGCTA TACTTATATC AACCCTCTCG 360 ACGGCACTTA TCCGCCTGGT ACTGAGCAAA ACCCCGCTAA TCCTAATCCT TCTCTTGAGG 420 AGTCTCAGCC TCTTAATACT TTCATGTTTC AGAATAATAG GTTCCGAAAT AGGCAGGGGG 480 CATTAACTGT TTATACGGGC ACTGTTACTC AAGGCACTGA CCCCGTTAAA ACTTATTACC 540 AGTACACTCC TGTATCATCA AAAGCCATGT ATGACGCTTA CTGGAACGGT AAATTCAGAG 600 ACTGCGCTTT CCATTCTGGC TTTAATGAAG ATCCATTCGT TTGTGAATAT CAAGGCCAAT 660 CGTCTGACCT GCCTCAACCT CCTGTCAATG CTGGCGGCGG CTCTGGTGGT GGTTCTGGTG 720 GCGGCTCTGA GGGTGGTGGC TCTGAGGGTG GCGGTTCTGA GGGTGGCGGC TCTGAGGGAG 780 GCGGTTCCGG TGGTGGCTCT GGTTCCGGTG ATTTTGATTA TGAAAAGATG GCAAACGCTA 840 ATAAGGGGGC TATGACCGAA AATGCCGATG AAAACGCGCT ACAGTCTGAC GCTAAAGGCA 900 AACTTGATTC TGTCGCTACT GATTACGGTG CTGCTATCGA TGGTTTCATT GGTGACGTTT 960 CCGGCCTTGC TAATGGTAAT GGTGCTACTG GTGATTTTGC TGGCTCTAAT TCCCAAATGG 1020 CTCAAGTCGG TGACGGTGAT AATTCACCTT TAATGAATAA TTTCCGTCAA TATTTACCTT 1080 CCCTCCCTCA ATCGGTTGAA TGTCGCCCTT TTGTCTTTGG CGCTGGTAAA CCATATGAAT 1140 TTTCTATTGA TTGTGACAAA ATAAACTTAT TCCGTGGTGT CTTTGCGTTT CTTTTATATG 1200 TTGCCACCTT TATGTATGTA TTTTCTACGT TTGCTAACAT ACTGCGTAAT AAGGAGTCTT 1260 AATGACTCTA GAGGTCGAAA TTCACCTCGA AAGCAAGCTG ATAAACCGAT ACAATTAAAG 1320 GCTCCTTTTG GAGCCTTTTT TTTTGGAGAT TTTCAACGTG AAAAAATTAT TATTCGCAAT 1380 TCCAAGCTAA TTCACCTCGA AAGCAAGCTG ATAAACCGAT ACAATTAAAG GCTCCTTTTG 1440 GAGCCTTTTT TTTTGGAGAT TTTCAACGTG AAAAAATTAT TATTCGCAAT TCCAAGCTCT 1500 GCCTCGCGCG TTTCGGTGAT GACGGTGAAA ACCTCTGACA CATGCAGCTC CCGGAGACGG 1560 TCACAGCTTG TCTGTAAGCG GATGCAGATC ACGCGCCCTG TAGCGGCGCA TTAAGCGCGG 1620 CGGGTGTGGT GGTTACGCGC AGCGTGACCG CTACACTTGC CAGCGCCCTA GCGCCCGCTC 1680 CTTTCGCTTT CTTCCCTTCC TTTCTCGCCA CGTTCGCCAG CTTTCCCCGT CAAGCTCTAA 1740 ATCGGGGGCT CCCTTTAGGG TTCCGATTTA GTGCTTTACG GCACCTCGAC CCCAAAAAAC 1800 TTGATTAGGG TGATGGTTCA CGTAGTGGGC CATCGCCCTG ATAGACGGTT TTTCGCCCTT 1860 TGACGTTGGA GTCCACGTTC TTTAATAGTG GACTCTTGTT CCAAACTGGA ACAACACTCA 1920 ACCCTATCTC GGTCTATTCT TTTGATTTAT AAGGGATTTT GCCGATTTCG GCCTATTGGT 1980 TAAAAAATGA GCTGATTTAA CAAAAATTTA ACGCGAATTT TAACAAAATA TTAACGTTTA 2040 CAATTTGATC TGCGCTCGGT CGTTCGGCTG CGGCGAGCGG TATCAGCTCA CTCAAAGGCG 2100 GTAATACGGT TATCCACAGA ATCAGGGGAT AACGCAGGAA AGAACATGTG AGCAAAAGGC 2160 CAGCAAAAGG CCAGGAACCG TAAAAAGGCC GCGTTGCTGG CGTTTTTCCA TAGGCTCCGC 2220 CCCCCTGACG AGCATCACAA AAATCGACGC TCAAGTCAGA GGTGGCGAAA CCCGACAGGA 2280 CTATAAAGAT ACCAGGCGTT TCCCCCTGGA AGCTCCCTCG TGCGCTCTCC TGTTCCGACC 2340 CTGCCGCTTA CCGGATACCT GTCCGCCTTT CTCCCTTCGG GAAGCGTGGC GCTTTCTCAA 2400 TGCTCACGCT GTAGGTATCT CAGTTCGGTG TAGGTCGTTC GCTCCAAGCT GGGCTGTGTG 2460 CACGAACCCC CCGTTCAGCC CGACCGCTGC GCCTTATCCG GTAACTATCG TCTTGAGTCC 2520 AACCCGGTAA GACACGACTT ATCGCCACTG GCAGCAGCCA CTGGTAACAG GATTAGCAGA 2580 GCGAGGTATG TAGGCGGTGC TACAGAGTTC TTGAAGTGGT GGCCTAACTA CGGCTACACT 2640 AGAAGGACAG TATTTGGTAT CTGCGCTCTG CTGAAGCCAG TTACCTTCGG AAAAAGAGTT 2700 GGTAGCTCTT GATCCGGCAA ACAAACCACC GCTGGTAGCG GTGGTTTTTT TGTTTGCAAG 2760 CAGCAGATTA CGCGCAGAAA AAAAGGATCT CAAGAAGATC CTTTGATCTT TTCTACGGGG 2820 TCTGACGCTC AGTGGAACGA AAACTCACGT TAAGGGATTT TGGTCATGAG ATTATCAAAA 2880 AGGATCTTCA CCTAGATCCT TTTAAATTAA AAATGAAGTT TTAAATCAAT CTAAAGTATA 2940 TATGAGTAAA CTTGGTCTGA CAGTTACCAA TGCTTAATCA GTGAGGCACC TATCTCAGCG 3000 ATCTGTCTAT TTCGTTCATC CATAGTTGCC TGACTCCCCG TCGTGTAGAT AACTACGATA 3060 CGGGAGGGCT TACCATCTGG CCCCAGTGCT GCAATGATAC CGCGAGACCC ACGCTCACCG 3120 GCTCCGCTTT TATCAGCAAT AAACCAGCCA GCCGGAAGGG CCGAGCGCAG AAGTGGTCCT 3180 GCAACTTTAT CCGCCTCCAT CCAGTCTATT AATTGTTGCC GGGAAGCTAG AGTAAGTAGT 3240 TCGCCAGTTA ATAGTTTGCG CAACGTTGTT GCCATTGCTG CAGGCATCGT GGTGTCACGC 3300 TCGTCGTTTG GTATGGCTTC ATTCAGCTCC GGTTCCCAAC GATCAAGGCG AGTTACATGA 3360 TCCCCCATGT TGTGCAAAAA AGCGGTTAGC TCCTTCGGTC CTCCGATCGT TGTCAGAAGT 3420 AAGTTGGCCG CAGTGTTATC ACTCATGGTT ATGGCAGCAC TGCATAATTC TCTTACTGTC 3480 ATGCCATCCG TAAGATGCTT TTCTGTGACT GGTGAGTACT CAACCAAGTC ATTCTGAGAA 3540 TAGTGTATGC GGCGACCGAG TTGCTCTTGC CCGGCGTCAA CACGGGATAA TACCGCGCCA 3600 CATAGCAGAA CTTTAAAAGT GCTCATCATT GGAAAACGTT CTTCGGGGCG AAAACTCTCA 3660 AGGATCTTAC CGCTGTTGAG ATCCAGTTCG ATGTAACCCA CTCGTGCACC CAACTGATCT 3720 TCAGCATCTT TTACTTTCAC CAGCGTTTCT GGGTGAGCAA AAACAGGAAG GCAAAATGCC 3780 GCAAAAAAGG GAATAAGGGC GACACGGAAA TGTTGAATAC TCATACTCTT CCTTTTTCAA 3840 TATTATTGAA GCAGACAGTT TTATTGTTCA TGATGATATA TTTTTATCTT GTGCAATGTA 3900 ACATCAGAGA TTTTGAGACA CAACAGATCT GGCCATCATG ATGGAATGTT TCCCCGGTGG 3960 TGTTATCTGG CAGCAGTGCC GTCGATAGTA TGCAATTGAT AATTATTATC ATTTGCGGGT 4020 CCTTTCCGGC GATCCGCCTT GTTACGGGGC GGCGACCTCG CGGGTTTTCG CTATTTATGA 4080 AAATTTTCCG GTTTAAGGCG TTTCCGTTCT TCTTCGTCAT AACTTAATGT TTTTATTTAA 4140 AATACCCTCT GAAAAGAAAG GAAACGACAG GTGCTGAAAG CGAGCTTTTT GGCCACGATG 4200 CGTCCGGCGT AGAGGATCTC TCACCTACCA AACAATGCCC CCCTGCAAAA AATAAATTCA 4260 TATAAAAAAC ATACAGATAA CCATCTGCGG TGATAAATTA TCTCTGGCGG TGTTGACATA 4320 AATACCACTG GCGGTGATAC TGAGCACATC AGCAGGACGC ACTGACCACC ATGAAGGTGA 4380 CGCTCTTAAA ATTAAGCCCT GAAGAAGGGC AGCATTCAAA GCAGAAGGCT TTGGGGTGTG 4440 TGATACGAAA CGAAGCATTG GAATTCTACA ACTTGCTTGG ATTCCTACAA AGAAGCAGCA 4500 ATTTTCAGTG TCAGAAGTCG ACCAAGGAGG TCTAGATAAC GAGGGCAAAA AATGAAAAAG 4560 ACAGCTATCG CGATTGCAGT GGCACTGGCT GGTTTCGCTA CCGTAGCGCA GGCC 4614 4657 base pairs nucleic acid single linear DNA (genomic) not provided 18 GGCGAGCTCC CGTGCAGCGG TCTTCAGCGC TTGCCGTCTG ACCGTAGCGC TGGAAGACGC 60 TCCAGAGGGT ACCCCGATAT CAGAGCTGAA ACTGTTGAAA GTTGTTTAGC AAAATCCCAT 120 ACAGAAAATT CATTTACTAA CGTCTGGAAA GACGACAAAA CTTTAGATCG TTACGCTAAC 180 TATGAGGGCT GTCTGTGGAA TGCTACAGGC GTTGTAGTTT GTACTGGTGA CGAAACTCAG 240 TGTTACGGTA CATGGGTTCC TATTGGGCTT GCTATCCCTG AAAATGAGGG TGGTGGCTCT 300 GAGGGTGGCG GTTCTGAGGG TGGCGGTTCT GAGGGTGGCG GTACTAAACC TCCTGAGTAC 360 GGTGATACAC CTATTCCGGG CTATACTTAT ATCAACCCTC TCGACGGCAC TTATCCGCCT 420 GGTACTGAGC AAAACCCCGC TAATCCTAAT CCTTCTCTTG AGGAGTCTCA GCCTCTTAAT 480 ACTTTCATGT TTCAGAATAA TAGGTTCCGA AATAGGCAGG GGGCATTAAC TGTTTATACG 540 GGCACTGTTA CTCAAGGCAC TGACCCCGTT AAAACTTATT ACCAGTACAC TCCTGTATCA 600 TCAAAAGCCA TGTATGACGC TTACTGGAAC GGTAAATTCA GAGACTGCGC TTTCCATTCT 660 GGCTTTAATG AAGATCCATT CGTTTGTGAA TATCAAGGCC AATCGTCTGA CCTGCCTCAA 720 CCTCCTGTCA ATGCTGGCGG CGGCTCTGGT GGTGGTTCTG GTGGCGGCTC TGAGGGTGGT 780 GGCTCTGAGG GTGGCGGTTC TGAGGGTGGC GGCTCTGAGG GAGGCGGTTC CGGTGGTGGC 840 TCTGGTTCCG GTGATTTTGA TTATGAAAAG ATGGCAAACG CTAATAAGGG GGCTATGACC 900 GAAAATGCCG ATGAAAACGC GCTACAGTCT GACGCTAAAG GCAAACTTGA TTCTGTCGCT 960 ACTGATTACG GTGCTGCTAT CGATGGTTTC ATTGGTGACG TTTCCGGCCT TGCTAATGGT 1020 AATGGTGCTA CTGGTGATTT TGCTGGCTCT AATTCCCAAA TGGCTCAAGT CGGTGACGGT 1080 GATAATTCAC CTTTAATGAA TAATTTCCGT CAATATTTAC CTTCCCTCCC TCAATCGGTT 1140 GAATGTCGCC CTTTTGTCTT TGGCGCTGGT AAACCATATG AATTTTCTAT TGATTGTGAC 1200 AAAATAAACT TATTCCGTGG TGTCTTTGCG TTTCTTTTAT ATGTTGCCAC CTTTATGTAT 1260 GTATTTTCTA CGTTTGCTAA CATACTGCGT AATAAGGAGT CTTAATGACT CTAGAGGTCG 1320 AAATTCACCT CGAAAGCAAG CTGATAAACC GATACAATTA AAGGCTCCTT TTGGAGCCTT 1380 TTTTTTTGGA GATTTTCAAC GTGAAAAAAT TATTATTCGC AATTCCAAGC TAATTCACCT 1440 CGAAAGCAAG CTGATAAACC GATACAATTA AAGGCTCCTT TTGGAGCCTT TTTTTTTGGA 1500 GATTTTCAAC GTGAAAAAAT TATTATTCGC AATTCCAAGC TCTGCCTCGC GCGTTTCGGT 1560 GATGACGGTG AAAACCTCTG ACACATGCAG CTCCCGGAGA CGGTCACAGC TTGTCTGTAA 1620 GCGGATGCAG ATCACGCGCC CTGTAGCGGC GCATTAAGCG CGGCGGGTGT GGTGGTTACG 1680 CGCAGCGTGA CCGCTACACT TGCCAGCGCC CTAGCGCCCG CTCCTTTCGC TTTCTTCCCT 1740 TCCTTTCTCG CCACGTTCGC CAGCTTTCCC CGTCAAGCTC TAAATCGGGG GCTCCCTTTA 1800 GGGTTCCGAT TTAGTGCTTT ACGGCACCTC GACCCCAAAA AACTTGATTA GGGTGATGGT 1860 TCACGTAGTG GGCCATCGCC CTGATAGACG GTTTTTCGCC CTTTGACGTT GGAGTCCACG 1920 TTCTTTAATA GTGGACTCTT GTTCCAAACT GGAACAACAC TCAACCCTAT CTCGGTCTAT 1980 TCTTTTGATT TATAAGGGAT TTTGCCGATT TCGGCCTATT GGTTAAAAAA TGAGCTGATT 2040 TAACAAAAAT TTAACGCGAA TTTTAACAAA ATATTAACGT TTACAATTTG ATCTGCGCTC 2100 GGTCGTTCGG CTGCGGCGAG CGGTATCAGC TCACTCAAAG GCGGTAATAC GGTTATCCAC 2160 AGAATCAGGG GATAACGCAG GAAAGAACAT GTGAGCAAAA GGCCAGCAAA AGGCCAGGAA 2220 CCGTAAAAAG GCCGCGTTGC TGGCGTTTTT CCATAGGCTC CGCCCCCCTG ACGAGCATCA 2280 CAAAAATCGA CGCTCAAGTC AGAGGTGGCG AAACCCGACA GGACTATAAA GATACCAGGC 2340 GTTTCCCCCT GGAAGCTCCC TCGTGCGCTC TCCTGTTCCG ACCCTGCCGC TTACCGGATA 2400 CCTGTCCGCC TTTCTCCCTT CGGGAAGCGT GGCGCTTTCT CAATGCTCAC GCTGTAGGTA 2460 TCTCAGTTCG GTGTAGGTCG TTCGCTCCAA GCTGGGCTGT GTGCACGAAC CCCCCGTTCA 2520 GCCCGACCGC TGCGCCTTAT CCGGTAACTA TCGTCTTGAG TCCAACCCGG TAAGACACGA 2580 CTTATCGCCA CTGGCAGCAG CCACTGGTAA CAGGATTAGC AGAGCGAGGT ATGTAGGCGG 2640 TGCTACAGAG TTCTTGAAGT GGTGGCCTAA CTACGGCTAC ACTAGAAGGA CAGTATTTGG 2700 TATCTGCGCT CTGCTGAAGC CAGTTACCTT CGGAAAAAGA GTTGGTAGCT CTTGATCCGG 2760 CAAACAAACC ACCGCTGGTA GCGGTGGTTT TTTTGTTTGC AAGCAGCAGA TTACGCGCAG 2820 AAAAAAAGGA TCTCAAGAAG ATCCTTTGAT CTTTTCTACG GGGTCTGACG CTCAGTGGAA 2880 CGAAAACTCA CGTTAAGGGA TTTTGGTCAT GAGATTATCA AAAAGGATCT TCACCTAGAT 2940 CCTTTTAAAT TAAAAATGAA GTTTTAAATC AATCTAAAGT ATATATGAGT AAACTTGGTC 3000 TGACAGTTAC CAATGCTTAA TCAGTGAGGC ACCTATCTCA GCGATCTGTC TATTTCGTTC 3060 ATCCATAGTT GCCTGACTCC CCGTCGTGTA GATAACTACG ATACGGGAGG GCTTACCATC 3120 TGGCCCCAGT GCTGCAATGA TACCGCGAGA CCCACGCTCA CCGGCTCCGC TTTTATCAGC 3180 AATAAACCAG CCAGCCGGAA GGGCCGAGCG CAGAAGTGGT CCTGCAACTT TATCCGCCTC 3240 CATCCAGTCT ATTAATTGTT GCCGGGAAGC TAGAGTAAGT AGTTCGCCAG TTAATAGTTT 3300 GCGCAACGTT GTTGCCATTG CTGCAGGCAT CGTGGTGTCA CGCTCGTCGT TTGGTATGGC 3360 TTCATTCAGC TCCGGTTCCC AACGATCAAG GCGAGTTACA TGATCCCCCA TGTTGTGCAA 3420 AAAAGCGGTT AGCTCCTTCG GTCCTCCGAT CGTTGTCAGA AGTAAGTTGG CCGCAGTGTT 3480 ATCACTCATG GTTATGGCAG CACTGCATAA TTCTCTTACT GTCATGCCAT CCGTAAGATG 3540 CTTTTCTGTG ACTGGTGAGT ACTCAACCAA GTCATTCTGA GAATAGTGTA TGCGGCGACC 3600 GAGTTGCTCT TGCCCGGCGT CAACACGGGA TAATACCGCG CCACATAGCA GAACTTTAAA 3660 AGTGCTCATC ATTGGAAAAC GTTCTTCGGG GCGAAAACTC TCAAGGATCT TACCGCTGTT 3720 GAGATCCAGT TCGATGTAAC CCACTCGTGC ACCCAACTGA TCTTCAGCAT CTTTTACTTT 3780 CACCAGCGTT TCTGGGTGAG CAAAAACAGG AAGGCAAAAT GCCGCAAAAA AGGGAATAAG 3840 GGCGACACGG AAATGTTGAA TACTCATACT CTTCCTTTTT CAATATTATT GAAGCAGACA 3900 GTTTTATTGT TCATGATGAT ATATTTTTAT CTTGTGCAAT GTAACATCAG AGATTTTGAG 3960 ACACAACAGA TCTGGCCATC ATGATGGAAT GTTTCCCCGG TGGTGTTATC TGGCAGCAGT 4020 GCCGTCGATA GTATGCAATT GATAATTATT ATCATTTGCG GGTCCTTTCC GGCGATCCGC 4080 CTTGTTACGG GGCGGCGACC TCGCGGGTTT TCGCTATTTA TGAAAATTTT CCGGTTTAAG 4140 GCGTTTCCGT TCTTCTTCGT CATAACTTAA TGTTTTTATT TAAAATACCC TCTGAAAAGA 4200 AAGGAAACGA CAGGTGCTGA AAGCGAGCTT TTTGGCCACG ATGCGTCCGG CGTAGAGGAT 4260 CTCTCACCTA CCAAACAATG CCCCCCTGCA AAAAATAAAT TCATATAAAA AACATACAGA 4320 TAACCATCTG CGGTGATAAA TTATCTCTGG CGGTGTTGAC ATAAATACCA CTGGCGGTGA 4380 TACTGAGCAC ATCAGCAGGA CGCACTGACC ACCATGAAGG TGACGCTCTT AAAATTAAGC 4440 CCTGAAGAAG GGCAGCATTC AAAGCAGAAG GCTTTGGGGT GTGTGATACG AAACGAAGCA 4500 TTGGAATTCT ACAACTTGCT TGGATTCCTA CAAAGAAGCA GCAATTTTCA GTGTCAGAAG 4560 TCGACCAAGG AGGTCTAGAT AACGAGGGCA AAAAATGAAA AAGACAGCTA TCGCGATTGC 4620 AGTGGCACTG GCTGGTTTCG CTACCGTAGC GCAGGCC 4657 

What is claimed is:
 1. A bank of genes, wherein said genes comprise a double-stranded DNA sequence which is represented by the following formula of one of their strands: 5′B₁B₂B₃ . . . B_(n)X_(n+1) . . . X_(n+a)Z_(n+a+1) Z_(n+a+2)X_(n+a+3) . . . X_(n+a+b)Q_(n+a+b+1) . . . Q_(n+a+b+J)3′ wherein n, a, b, and j are integers and are defined as: n>3, a>1, b>3 and j>1, wherein X_(n+1) . . . X_(n+a+b) is a hypervariable sequence and B represents any of bases adenine (A), cytosine (C), guanine (G) or thymine (T), X represents any of bases A, C, G or T, Z represents any of bases A, C, G or T, and Q represents any of bases A, C, G or T, wherein, (i) Z represents G or T at a G:T ratio of 1:1, and/or (ii) Z represents C or T at a C:T ratio of 1:1, and/or (iii) Z represents A or G at a A:G ratio of 1:1, and/or (iv) Z represents A or C at a A:C ratio of 1:1, and wherein subsequences B₁ . . . B_(n) and/or Q_(n+a+b+1) . . . Q_(n+a+b+j) represent recognition sites for restriction enzymes, and wherein the recognition sites are oriented such that their cleavage site upon cleavage generates a cohesive end including the two bases designated Z.
 2. A bank of genes according to claim 1, wherein each gene is provided as display vector, especially as M13 phage or M13 like phage or as phagemid.
 3. A set of four gene banks according to claim 1, wherein the gene banks are characterized as follows: a first gene bank in which Z represents G or T; a second gene bank in which Z represents C or T; a third gene bank in which Z represents A or G; and a fourth gene bank in which Z represents A or C.
 4. A set of four gene banks according to claim 3, wherein each gene is provided as display vector.
 5. A bank of genes, wherein said genes comprise a double stranded DNA sequence which is represented by the following formula of one of their strands: 5′B₁B₂B₃ . . . B_(n)X_(n)+₁ . . . X_(n+a)Z_(n+a+1)Z_(n+a+2)X_(n+a+3) . . . X_(n+a+b)Q_(n+a+b+1) . . . Q_(n+a+b+j)3′ wherein n, a, b and j are integers and n>3, a>1, b>3 and j>1, wherein X_(n+1) . . . X_(n+a+b) is a hypervariable sequence and B represents any one of bases A, C, G or T, X represents any one of bases A, C, G or T, Z represents any one of bases A, C, G or T, and Q represents any one of bases A, C, G or T, and wherein four set of oligonucleotide sequences comprising Z_(n+a+1) and Z_(n+a+2) are present, wherein the four sets are characterized as follows: (i) a first set in which Z_(n+a+1) represents G and Z_(n+a+2) also represents G; (ii) a second set in which Z_(n+a+1) represents C and Z_(n+a+2) represents T; (iii) a third set in which Z_(n+a+1) represents A and Z_(n+a+2) represents A or C, and (iv) a fourth set: Z_(n+a+1) represents T and Z_(n+a+2) represents C or G, and wherein sequences B₁ . . . B_(n) and/or Q_(n+a+b+1) . . . Q_(n+a+b+j) represent recognition sites for restriction enzymes, wherein the recognition sites are oriented such that their cleavage site upon cleavage generates a cohesive end including the two bases designated Z.
 6. A bank of genes according to claim 5, wherein the four sets of oligonucleotide sequences are present at a ratio of (i):(ii):(iii):(iv) of (0 to 1):(0 to 1):(0 to 1):(0 to 1) with the proviso that at least one of said sets is present.
 7. A bank of genes according to claim 5, wherein subsequences B₁ . . . B_(n) and/or Q_(n+a+b+1) . . . Q_(n+a+b+j) represent recognition sites for restriction enzymes and wherein the recognition sites are oriented such that their cleavage site upon cleavage generates a cohesive end including the two bases designated Z.
 8. A bank of genes wherein said genes comprise a double stranded DNA sequence which is represented by the following formula of one of their strands: 5′B₁B₂B₃ . . . B_(n)X_(n+1) . . . X_(n+a)Z_(n+a+1)Z_(n+a+2)X_(n+a+3) . . . X_(n+a+b)Q_(n+a+b+1) . . . Q_(n+a+b+j)3′ wherein n, a, b and j are integers and n>3, a>1, b>3 and j>1, wherein X_(n+1) . . . X_(n+a+b) is a hypervariable sequence and B represents any one of bases A, C, G or T, X represents any one of bases A, C, G or T, Z represents any one of bases A, C, G or T, and Q represents any one of bases A, C, G or T, and wherein the following six sets of oligonucteotide sequences comprising X_(n+a), Z_(n+a+1) and Z_(n+a+2) are present, wherein the six sets are characterized as follows: (i) a first set in which X_(n+a) represents A, G and/or T, or X_(n+a) represents C, G and/or T, Z_(n+a+1) represents G and Z_(n+a+2) represents G; (ii) a second set in which X_(n+a) represents A, C, G and/or T, Z_(n+a+1) represents C and Z_(n+a+2) represents T; (iii) a third set in which X_(n+a) represents A, C and/or G, Z_(n+a+1) represents A and Z_(n+a+2) represents A; (iv) a fourth set in which X_(n+a) represents A, C, G and/or T, Z_(n+a+1) represents A and Z_(n+a+2) represents C; (v) a fifth set in which X_(n+a) represents A, C, G and/or T, Z_(n+a+1) represents T and Z_(n+a+2) represents C; (vi) a sixth set in which X_(n+a) represents A, Z_(n+a+1) represents T and Z_(n+a+2) represents G, wherein B₁ . . . B_(n) and/or Q_(n+a+b+1) . . . Q_(n+a+b+j) represent recognition sites for restriction enzymes and wherein the recognition sites are oriented such that their cleavage site upon cleavage generates a cohesive end including the two bases designated Z.
 9. A bank of genes according to claim 8, wherein the six sets of oligonucleotide sequences are present at a ratio of (i):(ii):(iii):(iv):(v):(vi) of (0 to 1):(0 to 1):(0 to 1):(0 to 1):(0 to 1):(0 to 1) with the proviso that at least one of said sets is present.
 10. A bank of genes according to claim 5, wherein each gene is provided as display vector.
 11. A bank of genes according to claim 1, wherein the double stranded DNA sequence comprises a DNA region encoding a peptide or a protein to be displayed.
 12. A bank of genes according to claim 1, characterized in that n=j=6, a=14 and b=16.
 13. A bank of genes according to claim 1, wherein the restriction enzyme is a type II S restriction enzyme.
 14. A bank of genes according to claim 1, characterized in that: (a) subsequence B₁ . . . B_(n) is the recognition site for the restriction enzyme BpmI(CTGGAG) and Q_(n+a+b+1) . . . Q_(n+a+b+j) is an inverted BsgI recognition site (CTGGCAG); or (b) subsequence B₁ . . . B_(n) is the recognition site for the restriction enzyme BsgI recognition site (CTGGCAG) and Q_(n+a+b+1) . . . Q_(n+a+b+j) is an inverted BpmI (CTGGAG).
 15. A bank of genes according to claim 1, characterized in that the hypervariable sequence X_(n+1) . . . X_(n+a+b) contains NNB or NNK wherein N=adenine (A), cytosine (C), guanine (G) or thymine (T); B=cytosine (C), guanine (G) or thymine (T); and K=guanine (G) or thymine (T).
 16. Phage-display libraries or phagemid libraries, characterized by genes according to claim 1 and comprising an excess of 10⁶ variant clones.
 17. A phage-display library or a phagemid-display library according to claim 16 in the form of packaged particles.
 18. A phage-display library or a phagemid-display library according to claim 16 in the form of display vectors comprising Escherichia coli population(s). 